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Reactions to Light in 


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UNIVERSITY OF ILLINOTS LIBRARY 
HAL 


ysis JAN @ 2 1917 
Reactions to Light in Vanessa Antiopa, 


with Special Reference to 


Circus Movements 


“BY 


WILLIAM LEE DOLLEY, Jr. 


A Dissertation 


SUBMITTED TO THE BOARD OF UNIVERSITY STUDIES OF THE JOHNS HOPKINS UNIVERSITY 
IN CONFORMITY WITH THE REQUIREMENTS FOR THE DEGREE OF 


DOCTOR OF PHILOSOPHY 


1914 


BALTIMORE : 
1916 





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UNIVERSITY OF ILI INOIS LIBRARY 
JAN 31 1917 


Reprinted from Tue JOURNAL OF EXPERFMENTAL ZOOLOGY, Vol. 20, No. 3, 
: April, 1916 


REACTIONS TO LIGHT IN VANESSA ANTIOPA, WITH 
SPECIAL REFERENCE TO CIRCUS MOVEMENTS 
WILLIAM L. DOLLEY, Jr. 

Professor of Biology, Randolph-Macon College 
From the Zoélogical Laboratory of The Johns Hopkins University 


TWENTY-ONE FIGURES 


CONTENTS 

ELEMIS Mey Pet eee a aH co s'E6 SE Fe aS ENS on CSN d io wiw Be ODT 
RECEP E SEde nro RAIA 2 UR Act cia chy te < dale see sicvid aia dette R eam dald slccles 367 
SE ES EE IOSEL OSB TES foe ae. weeseis Gin op less. 9 oss wine es Abn Wie. os wis bsp Bask tho 370 
Behavior of specimens with but one functional eye....................... 371 
A. Behavior in normal conditions of illumination........................ 371 
me Genaviorin a beam ‘of-lighti.8 (0. co2.c.. cdi eee OF rd] PRE ae 371 

1. Description of reactions—deflection, circus movements and orien- 
SOONG Ss ig So RE Ae Oe ae eae ys a 371 

2. Relation between the degree of curvature in circus movements and 
Lee ULENELGY fac sadayhe Gt he Peek: c's (eae eRe e ee 382 

3. Relation between the angle of deflection and the luminous inten- 
SU loeione Jon lc Ggot ae erun ke Geee Cec ee nn ene en Coe 5 era 383 
a. Effect of beginning the trials in different intensities........ 383 

b. Effect of sudden changes of intensity on the angle of deflec- 
SIU Pane OR eis a ae 4) cE Ae ths Pas PU bb de dated dies « 386 
4. Reorientation after changing the direction of the beam of light.. 389 
>. Effect of the covering of the eye owing to contact................... 394 
SRIRESOHANION I NOR-CureCtL VG: MENG... shen eee Teens ces ccna eneeeeees ts 399 

E. Relation between the degree of curvature in circus movements and the 
luminous intensity of non-directive light.......................... 404 
an titect OF INNMINAtING ONLY ONG CVO... 45.65 caus wend se veh aren Wyma 410 
1. Effect of illuminating the entire surface of one eye.............. 410 
2. Effect of illuminating different areas of one eye................. 413 
See OIDINATY ANG CONCLUSIONIAS sac 5 in vata sid sata daWinn dandy dite tint tn =’ 415 
NEON MLC el oer cc Sister, id Tete PHY ah oa Risley 06 W's, 5 MGR wha, Magda taialads des 419 

INTRODUCTION 


One of the most thorough pieces of work, which have been 
done on the reactions to light itt butterflies, is that reported by 
Parker (’03) on the mourning-cloak butterfly, Vanessa antiopa. 

357 


308 WILLIAM L. DOLLEY, JR. 


This investigator found that these butterflies are highly positive 
in their reactions to light, but that when they come to rest in 
bright sunlight they ordinarily orient with the head directed 
away from the source of light. He found, however, that when 
one eye is painted black they do not orient, but continuously 
creep or fly in curves with the functional eye toward the center. 
Such reactions are usually called circus movements. This be- 
havior, the author asserts (p. 463), is in accord with the view 
‘“‘that the orientation of an organism in light is dependent upon 
the equal stimulation of symmetrical points on its body.” 

A number of other investigators have, also, recorded experi- 
ments with other organisms in which circus movements have 
been observed. Reactions of this nature have been reported in 
experiments of three sorts: those in which one eye has been pre- 
vented from functioning, either by being blackened, or by being 
injured; those in which one antenna has been removed; and those 
in which certain parts of the brain or of the inner ear have been 
destroyed. . 

In these experiments it has been found that photo-positive 
animals, usually turn continuously toward the functional eye, 
while photo-negative animals usually turn in the opposite direc- 
tion. This is especially true in those cases in which one eye 
has been covered. Holmes (’01 and ’05) and his students, 
McGraw (13) and Brundin (’13), maintain that they have 
observed this behavior in the following organisms: Hyalella den- 
tata, Talorchestia longicornis, Orchestia agilis, two species of 
bees, the robber fly, Asilus, Tabinus, a Syrphid, Ranatra, Noto- 
necta, several beetles, Stenopelmatus, three species of flies, a 
number of species of butterflies, and the amphipod, Orchestia 
pugettensis. In all these cases, positive animals turned toward 
the functional eye, while negative animals turned toward the 
covered eye. ‘This, however, was not found to be true in all of 
the species investigated. Holmes and McGraw (11, p. 370) 
state that several species of butterflies, among them Vanessa 
antiopa, frequently went in circles toward the covered eye, while 
Brundin (13 p. 346) maintains that in positive specimens of the 
amphipod, Orchestia traskiana, ‘“‘cireus movements will occur 





REACTIONS TO LIGHT IN VANESSA ANTIOPA 359 


as often toward the blackened eye as toward the normal eye.”’ 
Similar results have also been obtained with animals in which 
one eye was injured. Réadl (01, p. 458) extirpated one eye of 
the water scavenger beetle, Hydrophilus, and found that it de- 
flected toward the side of the injured eye. Hadley (’08, pp. 
180-199) seared with a hot needle the surface of one eye of larval 
lobsters in all stages of development, and maintains (p. 198): 
“The immediate results following this destruction of photo- 
reception in one eye are: (1) The production of rapid rotations, 
often at the rate of 150 per minute on the longitudinal axis of 
the body, which are invariably in a determined direction. (2) 
A type of progression in which the larva continually performs 
‘circus movements’ or turns toward the side of the injured eye.” 
Since these animals vary in the sign of their reaction to light at 
different stages of development, it is interesting to note that 
Hadley maintains that the circus movements made by animals 
of all ages were all in the direction of the blinded eye. Mast 
(10, p. 132) found that ‘‘Planaria with one eye removed, either 
by gouging it out or by cutting off one side of the anterior end 
obliquely, turn continuously from the wounded side for some 
time, evidently owing to the stimulation of the wound, since, 
after this is healed, they tend to turn in the opposite direction.”’ 

The destruction of the function of one eye is however not 
always followed by circus movements. Rddl (’03, pp. 58-64) 
states that Calliphora vomitoria is’ apparently not affected in 
its behavior by having one eye covered, while Musca domestica, 
although performing circus movements at times, can also ‘“‘run 
‘rather long distances in one direction.’’ Carpenter (’08, pp. 
483-491) blackened one eye of Drosophila ampelophila, and 
reported that now and then one performed circus movements, 
but he says (p. 486), ‘‘This conduct was exceptional, and was 
never persisted in except in the case of a single insect which had 
long been active and showed signs of fatigue.’’. They usually, 
however, deflected somewhat toward the functional eye as they 
proceeded toward the light. To quote further (p. 486), “‘They 
crept in a fairly direct path toward the light, although a ten- 
dency to deviate toward the side of the normal eye regularly 


360 WILLIAM L. DOLLEY, JR. 


occurred. The insects generally moved in a peculiar, jerky 
manner. The tendency to diverge from the direct path toward - 
the side of the uncovered eye was overcome by a series of short, 
quick turns in the opposite direction, which kept them headed 
toward the light.”” Mast (11, p. 222) found that the toad, Bufo 
americanus, with the lens removed from one eye, hops or walks 
toward a source of light, usually deflecting slightly toward the 
injured eye. Some individuals, however orient nearly, if not 
quite, as accurately after the operation as before. Thus, it is 
evident that there are numerous exceptions to the idea that the 
destruction of one eye is followed by circus movements. 

Moreover, it has been found that some animals which make 
circus movements modify their behavior after having had a cer- 
tain amount of experience, and move directly toward the light. 
Holmes (’05), in a detailed description of the behavior of one 
specimen of Ranatra with the right eye blackened, says that in 
the first ten trials before an electric light, it made many circus 
movements, and showed a ‘‘marked tendency to turn to the 
left.”’. In the next four trials it turned directly toward the 
source of light and in the succeeding ten trials it reached the 
light by a nearly straight path. After an interval of fifty min- 
utes, eleven more trials were made, ‘‘and it had not forgotten 
in the meantime how to reach the light by the most direct means,” 
for it went to the light in every case in a nearly straight course. 
The author also states that other specimens of Ranatra and 
Notonecta showed this same modification. Brundin (713, pp. 
334-352) observed similar reactions in the amphipods, Orchestia 
traskiana and Orchestia pugettensis, except that being negative’ 
the animals turned toward the blackened eye. Mast tested on 
two successive days a toad with one eye destroyed. He says 
(11, p. 222): ‘The following day this toad was again exposed: 
it now went toward the source of light even more nearly directly 
than on the preceding day.”’ Thus, it is clear that the reactions 
of at least some of these mutilated organisms may become modi- 
fied as the result of repeated trials. 

This is apparently not true of some animals. Rdadl cut out 
one eye of Hydrophilus, and states that, though it lived for 





REACTIONS TO LIGHT IN VANESSA ANTIOPA 361 


several weeks in an aquarium, it never moved in a straight line, 
but always in a course curved toward the side of the injured eye. 
He says (’01, p. 458): ‘‘Es hat darnach noch mehrere Wochen in 
meinem Aquarium gelebt, bewegte sich aber niemals gerade 
sondern immer nur in einem Bogen concav nach der Seite des 
extirpirten Auges.”’ This investigator (’03, p. 62) also observed 
a fly, Dexia carinifrons, on the second day after its eye was 
blackened and found its behavior was similar to that exhibited 
immediately after the eye was covered, that is, it moved con- 
tinually toward the functional eye. 

The second group of experiments, as previously stated, refer 
to insects with one antenna removed. V. L. Kellogg (’07, pp. 
152-154) removed the left antenna from a male silk worm moth, 
and found that when such an animal was placed three or four 
inches from a female it ‘‘moved energetically around in repeated 
circles to the right, or, rather, in a flat spiral, thus getting (usually) 
gradually nearer and nearer to the female.’’ Males with the 
right antenna removed turned continually to the left. In the 
same year, Barrows (’07, pp. 515-537) removed the terminal 
segment from one antenna of some fruit flies, Drosophila ampelo- 
phila, and then, after twenty-four hours without food exposed 
‘them to the odor of fermenting banana. He maintains that they 
moved in circles toward the uninjured antenna in all but a few 
cases in which they deflected in the opposite direction. 

The third group of experiments mentioned comprises those in 
which parts of the brain and inner ear have been injured or 
removed. In these cases it is also maintained that the animals 
make circus: movements. 

It ean thus be seen that great diversity exists among the results 
obtained by the various investigators in their experiments on 
animals with the sense organs on one side destroyed. Among 
these, those which refer to the eyes are of greatest immediate 
interest to us. In these experiments it was found that while 
photo-positive animals usually turn toward the functional eye 
and photo-negative animals toward the non-functional eye, some 
turn in the opposite direction and others orient fairly accurately, 


THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 20, No. 3 


362 WILLIAM L. DOLLEY, JR. 


while still others make circus movements for a period and then 
orient fairly accurately. 

This marked lack of harmony between the results obtained 
may in some measure, at least, be due to the fact that the num- 
ber of sources of light was not the same in all of the experiments: 
Parker does not state the conditions under which the specimen 
of Vanessa antiopa used by him made circus movements. Radl 
presumably performed his experiments before a window, i.e., 
under conditions in which the animals received some light from 
many different directions. The same probably held also for the 
work of Holmes on amphipods and .several insects. In some 
experiments, however, as in those performed with Ranatra and 
Notonecta, he worked in a ‘darkened room,’ and used for a source 
of light a sixteen candle-power incandescent lamp. Brundin and 
Carpenter also used a similar source of light. It is significant 
indeed that in every case where a single source of light on the 
same horizontal plane with the organism was used, at least some 
trials are described in which no circus movements were made, 
the animals moving in a fairly straight course toward the light. 
This was true of Ranatra, Notonecta, Drosophila, Bufo ameri- 
canus, Orchestia traskiana, and Orchestia pugettensis. On the 
contrary, in none of the experiments but one, where the light’ 
conditions were not sharply defined, have the investigators re- 
corded any other behavior than movements in circles. This 
single exception is that described by Radl, in which Calliphora 
vomitoria and Musca domestica with one eye blackened ran for 
some distance directly toward a window. 

The experiments described in the present paper show that in 
the case of Vanessa antiopa, at least, a knowledge of the number 
of sources of stimulation is of great importance in a discussion 
of circus movements; for the same animals, which, in a hori- 
zontal beam, moved toward the source of light in a fairly straight 
course, performed circus movements continuously when placed 
before a window, or when the single source of light was placed 
above the animal so that the light was non-directive.t The 


1 The term ‘non-directive light,’ as used in this paper, denotes diffuse illu- 
mination. 


REACTIONS TO LIGHT IN VANESSA ANTIOPA 363 


reactions under the former conditions seem to indicate that 
both eyes are necessary for orientation; those under the latter, 
that only one eye is necessary. Consequently, if the butterflies 
had been studied only in front of a window, the conclusions 
would necessarily have been erroneous. 

Circus movements have been held by many to have a very 
important bearing on the question as to the nature of the process 
of orientation. 

Holmes discusses this question rather fully. He takes the 
position that the performance of circus movements indicates a 
direct or indirect connection between the impulses set up by 
light in the two retinas and the tension of the muscles of the 
legs or appendages on the two sides of the body, and that this 
is a ‘“‘sort of mechanical reflex process.’’ To him the pleasure- 
pain theory explains those cases in which orientation occurs 
in these asymmetrical animals. He says (11, p. 54): ‘In most 
crustacea, as in most insects, orientation is effected through the 
unequal action of the appendages on the two sides of the body. 
In a form which is positively phototactic, ight entermg one eye 
sets up impulses, which, passing through the brain and nerve 
cord, cause, directly or indirectly, movements predominantly of 
flexion of the legs of the same side and of extension of the append- 
ages of the opposite side of the body. If this is a sort of mechani- 
cal process, we should expect that, in a positively phototactic 
form, if one eye were destroyed or blackened over, the animal 
would move continuously toward the normal side.’”? Mindful 
of the fact that the Ranatras and Notonectas in time straightened 
their courses, and followed the light nearly as precisely as if they 
had the use of both eyes, he also concludes that ‘‘ Phototaxis 
may fall, to a certain extent, under the pleasure-pain type of 
behavior. . . . . Light, in some animals, is followed much 
as an object of interest is pursued by a higher’ animal” (’11, 
p- 55). To these conclusions Brundin (’13) assents. 

According to Carpenter, the local action theory of tropisms 
would explain circus movements, were it not that some animals 
with one eye blackened can orient, as accurately as if both eyes 
were functional. The pleasure-pain theory, he holds, explains 


364 WILLIAM L. DOLLEY, JR. 


this behavior. He says (’08, p. 486): ‘‘It is clear that the tropism 
theory, with its assumption of local action of stimulus on the 
side exposed to its effect, does not furnish a complete explanation 
of these reactions. . . . . A ‘pleasure-pain’ reaction appears 
to inhibit and dominate a ‘tropic’ reaction.” 

To Radl, cireus movements are an evidence of inequality in 
the tension of the muscles on opposite sides of the body, pro- 
duced by the blackening of one eye. He says (’038, p. 63): ‘Bei 
einem Tier, dem ein Auge geschwiarzt wurde, erschlaffen etwas 
die Muskeln an der Ko6rperseite, wo das Auge nicht sieht; da sich 
nun die Muskeln der anderen Seite kraftiger bewegen, so erfolgt 
eine Bewegung in einer nach der Seite dieser stirker arbeitenden 
Muskeln gekriimmten Bahn.” 

Parker (’03, p. 463), as has been previously stated, maintains 
that the circus movements he observed in Vanessa antiopa are 
in accordance with the view ‘‘that the orientation of an organism 
in light is dependent upon the equal stimulation of symmetrical 
points on its body.” He says further: ‘‘Should the eyes be the 
parts stimulated, any interference with one of these ought to 
result in a disturbance of the direction of the butterfly’s loco- 
motion. Thus, if the cornea of one eye were blackened, the 
insect in locomotion, being positively phototropic, ought to move 
as though that eye were in shade, namely in a circle, with the 
unaffected eye toward the center.” 

To Barrows, who worked on the reactions of Drosophila to 
odors, circus movements can only be explained by the ‘tropism 
theory.’ He says (’07, p. 535): “It seems impossible to explain 
the movements under these conditions in any other way than on 
the basis of the tropism theory. This theory has been stated 
in several ways. As applied to chemical stimulation, Verworn 
(99, p. 429) declares: ‘The word chemotaxis is applied to that 
property of organisms that are endowed with the capacity of 
active movement by which, when under the influence of chemi- 
cal stimuli acting unilaterally, they move toward or away from 
the source of the stimulus.’ ” 

V. L. Kellogg (07) and Bohn (11) agree with Loeb, whose 
views are given in the next paragraph, and Bohn even cites 
circus movements as one of his criteria for tropisms. 


REACTIONS TO LIGHT IN’ VANESSA ANTIOPA 365 


Loeb (706, p. 140) attempts to refute any notion of a pleasure- 
pain type of behavior in lower organisms, and accepts the phe- 
nomenon of circus movements as a fact in support of his theory 
in explanation of the orientation of animals. This is discussed 
fully in the Mechanistic Conception of Life. (12, p. 35-62.) 
He holds that the orientation of animals is controlled unequivo- 
cally by external agents, and that in orientation to light, there 
are two essential factors, the continuous action of light and the 
symmetrical structure of the organisms. According to his view, 
which may be called the ‘continuous action theory,’ the tension 
of the muscles of the appendages on the two sides of the body is 
controlled through direct reflex arcs by the photochemical changes 
produced by light in the two retinas. He says (’12, p. 39): 
“When two retinae (or other points of symmetry) are iJluminated 
with unequal intensity, chemical processes, also of unequal in- 
tensity, take place in the two optic nerves (or in the sensory nerves 
of the two illuminated points). This inequality of chemical 
processes passes from the sensory to the motor nerves and even- 
tually to the muscles connected with them. We conclude from 
this that with equal illumination of both retinae the symmetrical 
groups of muscles on both halves of the body will receive equal 
chemical stimuli and thus reach equal states of contraction, while 
when the rate of reaction is unequal, the symmetrical muscles 
on one side of the body come into stronger action than those on 
the other side. The result of such an inequality of the action 
of symmetrical muscles of the two sides of the body is a change 
in the direction of movement on the part of the animal.” 

It is clear that in this theory it is assumed that light is effective 
in orientation through its continuous action, that after orienta- 
tion has occurred, light continues to stimulate the photosensitive 
areas, and through direct reflex arcs, continues to affect the 
muscles of the appendages on the two sides of the body. These 
assumptions, as stated above, are, according to Loeb, supported 
by the behavior of animals with the sense organs functional only 
on one side. He quotes Parker as follows (’06, p. 140): ‘‘ Loeb 
has pointed out that the orientation of an organism in light is 
dependent upon the equal stimulation of symmetrical points on 


366 WILLIAM L. DOLLEY, JR. 


its body. Should the eyes be the parts stimulated, any inter- 
ference with one of these ought to result in a disturbance of the 
direction of the butterfly’s locomotion. Thus, if the cornea of 
one eye were blackened, the insect in locomotion, being positively 
phototropic, ought to move as though that eye were in shade; 
namely, in a circle, with the unaffected eye toward the center.” 

Mast holds that the precision with which some organisms with 
but one functional eye perform circus movements appears to 
add support to the ‘continuous action theory,’ but he also says 
(11, p. 222), as a result of his work on the toad, ‘‘ These results 
show that, in this form and in all other forms which orient after 
one eye is destroyed, difference of effective intensity on opposite 
sides does not regulate orientation.” 

A glance at these various views shows that the movement of 
‘animals in circles when one eye is blackened, or when one antenna 
is removed, has been held by most of the investigators to support 
the view that the orientation of animals is in accord with the 
‘continuous action theory’ described above. This theory is op-. 
posed by one that may be called the ‘change of intensity theory,’ 
the adherents of which hold that in some organisms, at least, light 
does not produce orientation through its continuous action, but 
by stimuli dependent upon the time rate of change of intensity. 
According to this theory, an organism going toward a source 
of light, may turn to one side; but when this occurs, then, imme- 
diately the photosensitive surfaces are exposed to a change of 
intensity, and this causes a reaction which results in reorienta- 
tion, after which the orienting stimulus ceases. 

The chief points at issue between the two theories concern the 
following questions: (1) Does light function in orientation through 
its continuous action, or through a change of intensity? (2) 
Does an animal, when oriented, continue to be affected by the 
same stimulus that is effective in producing orientation? and 
(3) Is bilateral symmetry essential in the process? 

In view of the bearing that circus movements have on the 
theories as to the mechanism of normal orientation in animals, 
and in view of the conflicting results recorded by previous workers 
it seemed desirable to make a more thorough and a more extended 


REACTIONS TO LIGHT IN VANESSA ANTIOPA 367 


study of this phenomenon than has been done previously. More- 
over, such a study should throw light on the question as to 
whether or not the path of nerve impulses resulting in a given 
reaction can be altered, as well as on the very important prob- 
lem of modifiability in behavior in general. 

The mourning cloak butterfly, Vanessa antiopa, was chosen 
to begin with because the results secured with this animal by 
Parker are widely known and frequently quoted. This work is 
to be followed by a more general study of the phenomenon in 
question. 

Before entering upon a discussion of these experiments I wish 
to express my very sincere appreciation of the kindness of Pro- 
fessor S. O. Mast in suggesting this problem to me and in so 
unselfishly aiding me throughout the course of the work. 


METHODS 


The butterflies used were all reared in the laboratory from 
larvae secured from both the June and the August broods in 
Massachusetts, New York, and Pennsylvania. No difficulty was 
experienced in keeping them in excellent condition for long periods. 
They were kept in the laboratory in a large glass case, and fed 
on honey and a weak solution of maple syrup in water. At 
frequent intervals the insects were picked up and dropped on 
filter paper soaked in the latter sweet mixture. If the proboscis 
was not extended at once, it was uncoiled with a pin, and when 
once the tip touched the liquid, the animal continued to feed 
until its abdomen was swollen to an extent which seemed dan- 
gerous. Since these butterflies pass the winter in the imago 
state, it is not surprising that six specimens lived from August 
until the latter part of February. These were the survivors of 
a lot of about thirty which were received at the same time. 
Had proper care been taken, it is likely that nearly all would 
have. lived through the winter in the laboratory. The wings of 
the butterflies were-usually clipped to prevent their escape. This 
was in no wise injurious, for animals with clipped wings lived 
and thrived at well as those whose wings were intact, and they 
behaved in the same manner. 


368 WILLIAM L. DOLLEY, JR. 


As already stated, three methods have heretofore been used 
to preyent the functioning of one eye; extirpation, searing with 
a hot needle, and covering with asphalt varnish. The latter 
method was used exclusively in the present work, because it was 
believed that fewer disturbing factors would be introduced 
thereby. 

In the early part of the work, one eye was covered with one 
or two coats of the asphalt varnish. After having made some 
experiments with animals treated thus, it was found, to my sur- 
prise, that insects with both eyes covered in this way still oriented 
fairly precisely, and went toward the source of light. Thus it 
is evident that the varnish as used did not exclude all of the 
light. The eyes were then painted repeatedly until the coats 
were so thick as to be distinctly evident when the observer was 
several feet from the butterflies. Under these conditions the 
animals were indifferent to light. Warned by this experience, 
the blinded insects used in all future experiments were so treated 
that it seemed certain that the eye was in every case effectively 
covered. Moreover frequent examinations were made to make 
sure that the varnish had not cracked or fallen off; and new 
coats were from time to time applied to make assurance doubly 
sure. 

In work of this sort it is important that the varnish be of such 
nature that it does not injure the eye in any way. The effect 
of the covering was consequently repeatedly tested by removing 
it from the eyes after it had been on for some time. Insects 
thus tested behaved as did those whose eyes had not been 
blackened, showing no effect from the varnish. 

The supply stock of butterflies was ordinarily kept in a large 
cage which was four feet high, four feet long and two feet wide. 
This was fastened against a south window in such a way that 
the window formed one side of the enclosure. The opposite side 
was also of glass and faced a small laboratory room. The other 
two sides, the top, and the bottom, were of wood. Careful 
observations were made on the insects in this enclosure, from 
time to time, throughout the whole period over which the experi- 
ments extended. But a much more thorough investigation of 


REACTIONS TO LIGHT IN VANESSA ANTIOPA 369 


the behavior in light was made in a dark room under accurately 
controlled environmental conditions. In these experiments the 
animals ‘were exposed in a horizontal beam produced by means 
of a 110 volt Nernst glower. The glower was mounted in front 
of a small opening in a light-proof box that was painted dead 
black inside, so as to form a non-reflecting background. It was 
placed 10 cm. from and at the same level with the top of a table 
on which the animals were tested. By means of screens the 
light from the glower was so cut down as to produce a sharply 
defined beam of the size desired. The edges of this beam could 
be clearly seen on the black top of the table. This beam was 
the only light in the room, and this was in large part absorbed 
by means of dull black paper hung over the exposed walls. 
There was consequently very little ight in the room aside from 
that in the beam. Under these conditions therefore, the animals 
were exposed in a beam of light from a single, small and con- 
centrated source. 

The limits of this beam were very apparent in the dark room 
in which the experiments were made. ‘The nature of the source 
of light and the sharply defined character of the beam are im- 
portant, for experiments described later demonstrate that the 
behavior of animals with one eye blackened depends to a marked 
* extent upon whether there are one or more’ sources of light 
present. 

Not only was the behavior of the animals described by the 
observer, but the butterflies, themselves, were forced to make 
permanent records of their own behavior. This was done by 
allowing them to walk on sheets of paper which had been covered 
with soot from an oil lamp. These sheets measured 20 x 25 cm., 
but in some experiments, a number of them were placed side by 
side until the area was as large as desired. The tracings made 
by the insects were made permanent by means of a coat of 
shellac. The butterflies were frequently allowed to walk over 
the sheets of paper covered with soot, and then the same experi- 
ment was repeated without ‘the use of the blackened paper. 
The same results were secured in both cases. This shows that 
the behavior was not affected by the soot. This method of hav- 


370 WILLIAM L. DOLLEY, JR. 


ing the animals make permanent records of their own behavior 
is most valuable, for the records can be kept indefinitely and 
studied, thus giving opportunity to recognize many significant 
features which otherwise might have been overlooked at the time 
the experiments were performed. It would be of value, no doubt, 
to the keenest observer. 


BEHAVIOR OF NORMAL SPECIMENS 


In the study of normal animals in the cage referred to above, 
Parker’s observations were confirmed. It was found that the 
insects were highly positive in their reactions to light. During 
the day, in the absence of direct sunlight, they were usually in 
active movement, flying against the window. Occasionally an 
animal would fly around the cage, but this was exceptional. 
When at rest the butterflies were usually grouped on the window 
side of the cage, where they assumed various positions on the 
bottom of the window sash, some facing the light, others in a 
horizontal position at right angles with the rays, some hanging ° 
on the sash in a vertical position with their heads up, and others 
hanging with their heads down. 

When the sun was so situated that the butterflies were exposed 
directly to its rays, and they were undisturbed, they usually 
ceased their active movements and oriented very definitely. ~ 
They turned so as to face directly away from the sun and spread 
their wings to their fullest extent, exhibiting behavior similar 
to that described by Parker. This position was retained indefi- 
nitely unless the insects were disturbed. 

In a beam of light in the dark room the responses were quite 
different. In making observations under these conditions the 
animals were placed in the beam at various distances from the 
glower so that they faced the-source of light. As soon as they 
were released they usually darted directly toward the glower and 
continued until they reached the edge of the table. The insects 
were always found to be highly positive in all intensities in which 
they were tested. They never exhibited the slightest indication 
of negative reactions. ‘They never came to rest with the head 
directed from the light and the wings spread, as they usually 
did in direct sunlight. 


REACTIONS TO LIGHT IN VANESSA ANTIOPA 371 
BEHAVIOR OF SPECIMENS WITH BUT ONE FUNCTIONAL EYE 


A. BEHAVIOR IN NORMAL CONDITIONS OF ILLUMINATION 


In normal conditions of illumination the behavior of butter- 
flies with but one functional eye was very different from that 
described above. Such specimens were tested on the floor of 
the cage referred to previously, on a table before a window, and 
in a beam of light in the dark room. Before a window and on 
the floor of the cage it was found that whenever they moved 
they turned continuously toward the functional eye, exhibiting 
_ behavior similar to that described by Parker. The periods of 
activity, which in some cases lasted for several minutes, alter- 
nated with periods of rest in which the animals remained practi- 
cally motionless, as if recovering from fatigue. But the point 
that is of especial interest is that they continued to make circus 
movements from day to day, and that they did not learn to orient. 
Two insects with one eye blackened were kept for twenty-three 
days, and although they were observed many times each day no 
modification in their behavior was detected. In this respect, 
however, the reactions in a beam of light differed greatly. 


B. BEHAVIOR IN A BEAM OF LIGHT 


1. Description of reactions—deflection, circus movements, and 
orrentation 


Under the conditions of illumination described in the preced- 
ing paragraph, the animal receives light from all sides, and all 
the large areas of the functional eye are approximately equally 
illuminated in every position assumed by the insect. When 
exposed to the light in a beam the animal receives light from 
only one direction, and consequently every movement that is 
not directed toward the glower produces a change in the illumi- 
nation of different large areas of the uncovered eye. This may 
account for the difference in behavior observed under the two 
conditions of illumination. 

The behavior in a beam of light of Vanessa with one eye 
blackened was studied in 46 different individuals and many of 


ake WILLIAM L. DOLLEY, JR. 


these were tested on several successive days. In nearly all cases 
the animals were forced to record their reactions on carbon 
paper, as previously described. In all tests the butterflies were 
placed in the beam so that they faced the light directly. The 
results obtained varied considerably in different individuals and 
also in the same individual under different conditions. In some 
respects, however, there was but little variation. 

Nearly all of the butterflies tested turned toward the functional 
eye immediately after they were exposed, regardless of the 
luminous intensity or the axial position with reference to the 


Fig. 1 Reproduction of various trails made by different specimens of Vanessa 
with the left eye blackened when exposed in a beam froma Nernst glower. The 
diverging straight lines represent the limits of the horizontal beam. The arrows 
indicate the direction of motion. Their trails show that there is great variation 
in the reactions of different individuals under the same conditions. 


direction of the rays of light. Some of them continued to turn 
in this direction making repeated circus movements? (fig. 1, a 
and b) until they became fatigued and stopped, or until they 
reached the edge of the beam, where many turned sharply toward 
the glower and traveled along the edge of the beam toward 
the source of light, as is shown in figure 1, c. A few, however, 
did not turn toward the light when they reached the edge of the 
beam, but passed into the shaded region, continuing to make 
circus movements (fig. 1, e€). Others did not make circus move- 
ments, but turned until the longitudinal axis made a certain 


2 In the present paper the term ‘circus movements’ with no further explanation 
means continuous movement toward the functional eye. 


REACTIONS TO LIGHT IN VANESSA ANTIOPA 373 


angle with the rays of light, and then continued until they 
reached the edge of the beam. Here they usually turned sharply 
toward the glower and moved along the edge of the beam toward 
the source of light (fig. 1, f) but occasionally they continued to 
turn here and made circus movements (fig. 1, 7), and sometimes 
they did not respond at all when they reached the edge of the 
beam, but continued until they had passed into the shaded region 
from 2 to 5 em. when they usually turned and proceeded directly 
toward the glower, remaining in this region (fig. 1, g). Ona few 
occasions, however, they did not turn when they reached the 
edge of the beam, but proceeded on in the shaded region indefi- 
nitely (fig. 1, h). A few animals did not turn toward the func- 
tional eye, but oriented fairly accurately and walked toward the 
glower in a nearly straight course (fig. 1, k). Several specimens 
in some trials turned toward the blackened eye, crossed the beam, 
and on reaching the edge turned and walked along it toward the 
source of light (fig. 1, 7). 

Many insects, as the trials proceeded, showed an increase in 
accuracy of orientation. This was evident in three respects: (1) 
in the number of circus movements made, (2) in the angle of 
deflection, and (3) in the promptness with which they oriented 
at the edge of the beam. 

The above general description may perhaps be made clearer 
if the reactions of one organism are described in detail. This 
animal designated as butterfly 10/25-a (left eye blackened) was 
tested on three successive days. 

On the first day this butterfly was given twenty trials (fig. 2). 
In every one it turned toward the unblackened eye immediately 
upon being placed in the beam. In the first trial it crossed the 
beam at an angle of approximately 95 degrees with the rays of 
light, and passed into the shaded region. After it had gone 6 
em. in this region it turned to the left (the blinded eye) and 
walked toward the glower in a slightly zig-zag course, remaining, 
however, in the comparative darkness to the right of the beam. 
In the second trial, after crossing the beam at an angle of nearly 
80 degrees, it again went to a point 6 cm. beyond the edge of the 
beam, but then it turned sharply to the right (toward the func- 


374 ; WILLIAM L. DOLLEY, JR. 


tional eye) and performed a circus movement. ‘This was fol- 
lowed by a fairly straight course for 7.5 em. At this point the 
organism turned again to the right as if to make a circus move- 
ment but did not complete it, turning instead to the left toward 
the source of light. In the third trial the insect made a circus 
movement as soon as it was placed in the beam and then crossed 
the beam at an angle of about 95 degrees with the rays of light, 
and went 3 em. into the shaded region where it turned toward 
the blackened eye and moved in a course nearly parallel with 
the edge of the beam. In the fourth the behavior was like that 
in the preceding trial except that after the organism passed the 








Fig. 2 Reproduction of 20 successive trails made by butterfly 10/25-a (left 
eye blackened) on the first day of the tests. aand b, limits of horizontal beam of 
light; 1-20, trailsmade in successive trials; small arrows, direction of movement 
of animal; large arrows, direction of rays of light; illumination at x, 624 mc.;3 
at y, 250 mc. 


edge of the beam it did not turn toward the glower, but con- 
tinued on in a fairly direct course until it reached the edge of the 
table. In the fifth trial the butterfly continued across the beam 
at about the same angle as in the previous trials until it had 
gone 2.5 cm. beyond the edge. At this point it turned toward 
the blackened eye and moved fairly directly toward the glower. 
In the sixth the organism again made a circus movement imme- 
diately upon being placed in the beam. It then crossed the 
beam at right angles with the rays, and on reaching the right 


3 Throughout this paper the abbreviation ‘me.’ will be used to indicate meter- 
candles. , 


REACTIONS TO LIGHT IN VANESSA ANTIOPA 315 


edge, immediately turned toward the blackened eye and moved 
along the edge of the beam toward the glower. In the seventh, 
eighth, and in the twelfth to the nineteenth trials the behavior 
of the butterfly was essentially the-same as in the fifth, but it 
usually went further in the shaded region before turning toward 
the glower, this distance varying from 2.5 to 14cm. After orien- 
tation, however, it continued to move in all cases fairly directly 
toward the glower. In the tenth and third trials, the behavior 
was essentially similar. In the ninth, eleventh, and twentieth 
the reactions were also very much alike, the organism in each 
trial curving gradually toward the functional eye, in this way 
passing beyond the edge of the beam into the shaded region 
outside, and then coming back to the edge. again. On reaching 
the edge of the beam the second time the butterfly turned much 
more sharply toward the functional eye, thus completing a circus 
movement and at the same time arriving at the edge of the beam 
a third time. When this occurred, the insect turned toward the 
glower and moved along the edge of the beam toward the source 
of light. : 

These reactions in the trials on the first day of the tests show: 
(1) that Vanessa with but one functional eye tends to turn toward 
this eye when placed in a beam of light; (2) that it can orient; 
(3) that orientation does not usually occur in the beam, but 
does occur either at the edge of the beam or several centimeters 
beyond it; (4) that after circus movements have been performed 
in a given trial the animal often orients and moves directly toward 
the source of light; and (5) that a change in illumination seems 
to favor the performance of circus movements, since, out of 8 
circus movements, 4 were made almost immediately after the 
insect was placed in the beam and before it had reached the 
edge of the beam, 3 were made at the edge of the beam, and only 
1 was made elsewhere. 

On the second day in all of the first eight trials, except the 
fifth, the butterfly assumed an angle of about 90 degrees with 
the rays, and then traveled across the beam and into the shaded 
region for a distance of from 1.5 to 9 cm. where orientation 
occurred (fig. 3). In the fifth it continued on to the right in 


376 WILLIAM L. DOLLEY, JR. 


a moderately straight course until it fell off the table. The 
behavior in the next three trials was very much alike, the organ- 
ism performing a circus movement upon first being placed in the 
beam, and then, after having gone a few centimeters beyond the 
edge, it turned and went toward the glower. The eleventh trial 
is interesting in that, although the organism was started very 
much nearer to the glower, and consequently in much stronger 























Fig. 3 Reproduction of 34 successive trails made by butterfly 10/25-a (left 
eye blackened) on the second day of thetests. a and b, limits of horizontal beam of 
light; 1-34, trails made in successive trials; small arrows, direction of movement 
of animal; large arrows, direction of rays of light; illumination at x, 624 me.; 
at y, 250 me. 


light, it, after having performed a circus movement, deflected 
at an angle of only 40 degrees with the rays of light, while in 
several of the previous trials in which it had started further 
away from the source of light it deflected at a much greater 
angle. In the twelfth trial the butterfly made a circus move- 
ment when first started and then after having gone 1.5 em. 
beyond the edge of the beam it again performed a circus move- 


ws 


REACTIONS TO LIGHT IN VANESSA ANTIOPA old 


ment. This was followed by a zig-zag course nearly parallel 
with the edge of the beam. This circus movement is worthy 
of notice for it was made.in the shaded region outside the beam, 
when the animal was in very weak light. It should also be 
noted that the diameter of the curve made is very nearly the same 
as the diameter of the curve made in the beam in comparatively 
strong light, when the insect was first started in this trial. This 
peculiarity will be correlated later with the results of other experi- 
ments. In the thirteenth trial after performing a circus move- 
ment in the beam the organism continued to the right in a fairly 
straight course to the edge of the table. In the fourteenth a 
circus movement in the beam was made, and then the animal 
went 7 cm. beyond the edge and oriented, moving toward the 
glower. In the fifteenth it crossed the rays of light and made 
a circus movement to the right of the beam. It then went toward 
the glower in a fairly straight line, but before reaching the source 
of light it made another circus movement. In the sixteenth a 
circus movement was made to the right of the beam. This was 
followed by a zig-zag course toward the glower. The behavior 
in the succeeding eighteen trials was essentially similar to that 
described above. It should be noted, however, that in the 
twenty-fourth trial the butterfly after moving to the right until 
the edge of the beam was reached turned more sharply toward 
the functional eye at this point. It did not, however, perform 
a circus movement, but gradually turned to the left. This sharp 
turn toward the functional eye on reaching the edge of the beam 
seems to support the conclusion arrived at from the trials on the 
previous day, namely, that change in illumination tends to favor 
the performance of circus movements. 

These trials on the second day thus confirm strongly the con- 
clusions drawn from the reactions on the first day, and they show 
moreover that after a certain amount of experience the angle of 
deflection tends to decrease, for on the first day the average 
angle between the path of the butterflies and the rays of light 
was 100 degrees while on the second day it was only 89.5 degrees. 

The reactions on the third day (fig. 4) differed very markedly 
from those described for the first two days in several respects. 


THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 20, No. 3 


‘ 


378 WILLIAM L. DOLLEY, JR. 


In all but the fourth and fifth trials the organism turned toward ° 
the functional eye, crossed the beam at a definite angle which 
was smaller than on the preceding days, and, on. reaching the — 
edge of the beam, turned at once to the left and walked along 
this edge toward the glower. In the fourth trial it responded 
very much like a normal specimen, walking down the center of 
the beam in a fairly straight line. In the fifth it deflected toward 
the blackened eye. No circus movements were made in any of 
the trials on this day. 











Fig. 4 Reproduction of 23 successive trails made by butterfly 10/25-a (left ~ 
eye blackened) on the third day of the tests. a and b, limits of horizontal beam 
of light; 1-23, trails made in successive trials; small arrows, direction of movement 
of animal; large arrows, direction of rays of light; illumination at x, 906 me.; at 
y, 266 mc. Compare figures 2, 3 and 4 and note that the insect on the third day 
made no circus movements, while on the two preceding days, it made numerous 
ones. Note also that the angle at which it deflected with the rays of light 
decreased. 


By comparing all of the reactions observed during the three 
days it will be seen that modification occurred in three different 
respects, as follows: (1) On the first two days there were numer- 
ous circus movements; on the third day there were none what- 
ever; (2) On the first two days the butterfly usually passed into 
the shaded region a considerable distance before it turned and 
went toward the glower; on the third day it turned toward the 
glower promptly on reaching the edge of the beam; (8) The 
angle of deflection was greatest on the first day and least on the 
third, the average angle at the edge of the beam for the three 
days being respectively 100, 89.5, and 41.5 degrees. The reac- 


REACTIONS TO LIGHT IN VANESSA ANTIOPA 379 


tions of three other insects showing similar behavior are pre- 
sented in figures 5, 6 and 7. 

The results presented in these figures as well as in the preced- 
ing ones seem to show that butterflies with but one functional 
eye improve in the accuracy of orientation with experience. This 
conclusion and others are strongly supported by the results 











yh tl 





t 
t yO obi lalz 


Fig.5 Reproduction of 15 successive trails made by butterfly 7/29-c (right eye 
blackened). a and 6, limits of horizontal beam of light; 1-15, paths made in 
successive trials; small arrows, direction of movement of animal; large arrows, 
direction of rays of light; illumination at z, 4892 mc.; at y, 544 mc. Note that 
this insect made three circus movements in the first four trials, while in the next 
eleven trials it made none. 


obtained in all of the tests made. These are briefly summarized 
in table 1. 

This table will be clearer if a brief explanation of some of the 
data is given. In the columns headed ‘Direction turned’ is 
stated the direction toward which the butterflies turned 7mmedi- 
ately after they were placed in the beam. The average angle 
of deflection was ascertained in the following way. The angle 


380 WILLIAM L. DOLLEY, JR. 


between the rays of light and the trail of the insect at the edge 
of the beam in each of the trials was measured. ‘This angle is 
termed the ‘angle of deflection.’ The average then was com- 
puted for a number of the first trials on each day, this number — 
being equal to the number of trials on that day on which fewest 
trials were given. The columns marked ‘Place where orientation 





Fig.6 Reproduction of 40 trails made by butterfly 10/1-b (left eye blackened). 
A, 1-20, trails made in successive trials on the first day of the tests; B, 1-20, trails 
made on the second day of the tests; a and b, limits of horizontal beam of light; 
small arrows, direction of movement of animal; large arrows, direction of rays 
of light; illumination at x, 925 mc.; at y, 266 mc. Note that this insect modified 
its reactions in that it made numerous circus movements in the trials on the 
first day, but made none in the trials on the second day. 


occurred’ also demand some explanation. By ‘Orientation’ is 
meant the assumption of an axial position with the head pointed 
directly toward the glower followed by movement in this direc- 
tion. If the animal turned and moved directly toward the source 
of light before it reached the edge of the beam it is said to have 
oriented ‘in the beam.’ If it, however, went more than one centi- 
meter beyond the edge before it turned toward the glower it is 


. 








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TABLE 1 


Summary of reactions in a beam of light of 46 specimens of Vanessa antiopa with but one functional eye 















































































































































DISTANCD NUMBER OF PLACD WHERE 
rH GLOWER OREN ORG gornicans ORIENTATION OCCURRED 
DESIGNATION IN TOTAL AveRkGm | — pees oh 
a aa brittle Svs see Ie, oe N 
Som ete a PER DAY besa Toward] nig not] In |Outside| PEFEECTION | In aes te als a Ne 
TRIALS WERE tional |°°Vee4] “turn | beam | beam beam | of | a iiton ae 
BHGUN eye eye beam 
October 
13 23-45 21 Left 21 0 0 31 1 99.0 0 9 10 2 
10/13-a..... u 23-45 22 Left 22 0 0 1 0 65.0 0 19 2 1 
15 23-45 21 Left 21 0 0 1 1 60.0 0 18 2 1 
16 23-45 21 Left 19 0 2 0 0 35.0 0 19 0 2 
October 
13 23-45 22 Right 22 0 0 72 5 97.0 0 16 5 1 
10/18-b..... 4 23-45 7 Right 7 0 0 1 0 100.0 0 4 3 0 
15 23-45 20 Right 20 0 0 28 2 81.4 0 il 4 5 
7 23-45 20 Right 20 0 0 1 0 69.2 1 4 13 2 
October 
10/l4-a..... 14 25-60 21 Left 21 0 0 8 0 78.2 0 19 1 1 
15 18-45 21 Left 21 0 0 0 0 54,2 0 20 1 0 
17 20-45 20 Left 20 0 0 0 0 43,2 0 20 0 0 
October 
10/25-a..... 25 28-45 20 Right 20 0 0 4 4 100.0 0 4 15 1 
26 28-45 34 Right 34 0 0 4 4 89.5 0 4 24 6 
27 15-43 23 Right 22 0 1 0 0 41.5 1 18 3 1 
October 
Tbjacse 6 23-45 20 Left 20 0 0 18 0 101.2 ) 10 5 5 
ae 7 25-80 20 Left 15 5 0 0 0 30.0 4 re) 4 0 
8 28-80 20 Left 10 9 1 0 0 14.7 0 14 0 6 
October 
10/1-a...... } 1 28-45 41 Left 41 0 0 25 30 78.0 2 0 1 38 
2 28-45 30 Left 28 1 1 0 5 50.0 1 ll 0 18 
October 
2 23-45 20 Left 20 0 0 2 0 81.8 0 4 11 5 
pa ‘ 25-45 20 Left 19 0 1 0 0 37.5 3 12 4 1 
4 23-45 21 Left 21 0 0 0 0 54.3 2 18 1 0 
5 18-45 20 Left 0 20 0 0 0 46,2 0 19 0 1 
6 20-47 21 Left 16 5 0 0 0 42.5 0 21 0 0 
July 
24 30 21 Left 18 2 1 0 2 62.0 3 8 4 6 
7/24-4-a... 25 30 35 Left 29 4 2 0 0 49.0 3 14 4 14 
26 30 10 Left 7 2 1 0 0 31.5 i 6 0 3 
27 30 10 Left 7 0 3 0 0 23.5 3 7 0 0 
July 
7/11-3 ll 30 21 Left 19 2 0 0 1 44.2 0 it 0 20 
he 12 “30 51 Left 45 6 0 0 0 35.0 2 4 6 39 
13 30 40 Left 15 8 17 0 0 11.0 19 itt 2 8 
October 
10/8-c..... 7 8 18-78 22 Left 22 0 0 0 2 44,3 0 15 5 
9 28-82 23 Left 19 at 3 0 0 14.5 3 19 0 1 
October 
10/24-a..... 4 24 25-82 20 Left 19 0 1 17 0 110.7 0 16 0 4 
25 25-65 21 Left 21 0 0 98 3 88.5 0 9 5 7 
October 
10/14-b } 14 18-45 33 Right 31 2 0 22 3 86.3 0 19 10 4 
‘eee 15 18-45 20 Right 19 0 if 17 2 83.0 2 14 0 4 
L 16 18-45 21 Right 21 0 0 2 i 0 ll 10 0 
September 
9/21-8 21 18-28 5 Right 5 0 0 1 0 107.0 0 2 3 0 
3° ae 22 28-45 10 Right 10 0 0 0 0 53.0 0 10 0 0 
23 23 Right 23 0 0 0 0 0 23 0 0 
October 
10/8-a...... 4 8 40 Left 38 1 1 0 1 71.5 8 28 3 1 
9 20 Left 18 2 0 0 0 29.75 0 19 0 1 
July 
7/16-0..... 16 30 17 Left 17 0 0 0 3 62.3 2 14 1 0 
July 
7/29-c....+. 29 30 15 Left 7 0 8 0 3 20.6 8 6 1 0 
September 
22 30 25 Right 25 0 0 0 0 67.5 0 3 16 6 
23 30 21 Right 20 1 0 0 0 62.5 0 il 9 1 
24 45 20 Right 9 9 2 1 0 25.5 2 15 1 2 
9/22-c..... 4 25 23-45 20 Right 20 0 0 0 0 62.0 0 20 0 0 
26 23-45 21 Right 21 0 0 f 3 79.0 0 13 0 8 
27 25-45 26 Right 26 0 0 0 0 51.5 0 26 0 0 
29 23-45 32 Right 32 0 0 0 0 51.0 0 32 0 0 
30 17-45 32 Right 32 0 0 0 0 57.2 1 29 2 0 
September 
22 28 45 Left 45 0 0 1 2 85.7 0 1 18 26 
24 45 20 Left 20 0 0 1 5 39.2 0 12 1 vf 
9/22-b 25 45 21 Left 14 2 5 0 0 34.7 5 10 4 2 
aie a 26 23-45 33 Left 31 0 2 1 0 60.7 2 9 15 - 7 
27 20-45 36 Left 32 0 4 0 0 40.5 4 32 0 0 
29 23-45 20 Left 20 0 0 2 0 A 0 13 4 3 
30 18-45 30 Left 28 1 1 0 0 56.0 1 19 9 1 
October 
1 23-43, 20 Right 20 0 0 9 2 67.7 0 9 9 2 
2 23-45 20 Right 19 st 0 0 0 41.5 0 16 4 0 
10/1-b 3 23-43 20 Right 20 0 0 0 0 55.2 0 12 7 1 
ra Bk 4 23-45 20 Right 20 0 0 0 0 68.7 0 18 2 0 
5 23-45 21 Right 21 0 0 0 0 63.2 0 19 2 0 
6 23-80 24 Right 24 0 0 0 0 36.0 0 24 0 0 
7 20-80 27 Right 26 1 0 0 0 33,7 0 26 0 a 
July 
7/8-3 8 30 73 Left 58 10 5 3 10 36.5 11 17 16 29 
A Sareea A) 9 30 58 Left 51 4 3 3 14 51.0 4 9 8 37 
10 30 33 Left 18 8 7 0 3 16.3 if 20 0 6 
September 
: 22 30 25 Left 24 1 0 0 3 69.2 0 0 17 8 
9/22-0..... 4 23 30 20 Left 20 0 0 0 0 57.5 0 7 13 0 
24 45 20 Left 20 0 0 0 1 68.0 0 u 9 0 
25 25-45 20 Left 20 0 0 0 0 69.0 0 10 10 0 
September 
: 22 30 25 Right 25 0 0 1 0 82.0 0 ll 14 0 
23 30 20 Right 15 2 3 0 0 19.0 11 8 0 1 
24 40-45 20 Right 20 0 0 0 0 43.0 0 20 0 0 
9/22-d..... { 25 20-42 20 Right 20 0 0 1 0 68.0 0 20 0 0 
26 28-45 20 Right 0 0 20 0 0 20 0 0 0 
27 18-45 22 Right 21 1 0 1 0 44.0 0 21 0 1 
29 18-45 2 Right 20 0 0 0 0 48.0 0 20 0 0 
30 | 23-45 10 Right 5 5 0 0 0 0 10 0 0 
October 
2 23-45 22 Right 22 0 0 0 0 71.0 0 13 5 4 
3 25-45 20 Right 20 0 0 1 6 73.0 0 4 7 9 
1O/d-0, 25 -.,- 4 18-45 23 Right 22 1 0 0 0 68.0 0 13 7 3 
5 15-45 21 Right 21 0 0 0 0 68.0 1 15 4 1 
6 13-78 22 Right 14 6 2 0 0 27.0 5 13 1 3 
7 20-80 24 Right 19 5 0 0 0 43.0 0 23 0 1 
July 
ot 30 36 Left 32 1 3 0 0 26.5 4 23 5 4 
22 20-28 35 Left 23 11 1 0 0 65.0 2 27 3 3 
7/21-6..... | 23 28 31 Left 16 13 2 0 0 47.0 4 11 6 10 
24 20-28 13 Left 13 0 0 0 0 56.5 0 8 2 3 
| 25 28 14 Left 13 0 1 0 0 64.5 1 7 3 3 
l 26 28 11 Left 10 0 1 0 0 58.0 0 0 4 7 
July | 
24 30 10 Left 10 0 0 0 0 28.0 0 10 0 0 
7/24-4..... 25 30 11 Left ll 0 0 0 0 35.0 0 ll 0 0 
26 30 nb Left il 0 0 0 0 33.0 0 ll 0 0 
27 30 11 Left Il 0 0 0 0 0 10 0 1 
September 
24 30-60 50 Left 39 7 4 7 17 59.0 9 10 1 30 
0/24-a..... 4 25 25-60 20 Left 19 if 0 0 0 79.0 0 14 5 1 
26 25-45 31 Left 30 0 1 9 3 77.0 1 16 9 5 
27 23-45 20 Left 20 0 0 5 6 64.0 0 10 4 6 
July 
23 30 11 Left 11 0 0 0 0 29.3 0 11 0 0 
7/28-4...0. 24 30 rT Left 11 0 0 0 0 36.2 0 11 0 0 
| 25 30 8 Left 8 0 0 0 0 26.2 0 8 0 0 
26 30 ll Left 11 0 0 0 0 31.2 0 10 1 0 
July 
11 30 51 Right 48 2 1 0 0 31.0 12 ri 17 15 
T/l1-4..... 12 30 75 Right 71 0 4 0 0 50.8 7 8 13 47 
13 30 32 Right 30 0 2 0 0 37.6 4 14 Ny 13 
14 30 30 Right 27 0 3 0 0 52.5 3 4 ll 12 
July 
5 | 23 30 18 Left 16 2 0 1 0 33.5 4 if 2 5 
7/23-40.... 4 24 30 10 Left 10 0 0 0 0 24.5 2 6 0 2 
25 30 10 Left 9 1 0 0 0 31.5 0 8 2 0 
26 30 10 Left 10 0 0 0 0 37.0 0 8 1 1 
July 
T/2G-Biasvas'e'ds 29 30 16 Left il 0 5 0 0 20.3 8 8 0 0 
July 
G/B Deter 16 30 23 Left 23 0 0 0 2 45.6 7 3 0 13 
July 
7/16-ph...... 16 30 12 Left 11 1 0 0 1 50.8 0 4 2 6 
July 
7/20-d....0+« 29 30 10 Left 1 1 8 0 0 11.0 8 1 1 0 
July 
C/20-D saeuln a 29 30 13 Left 7 2 4 0 0 18.0 5 4 2 2 
July 
7/16-b....% +. 16 30 20 Left 16 0 4 0 1 27.2 4 14 2 C) 
July 
7/16-0.5 eee 16 30 18 Left 0 8 10 0 0 16 1 0 i 
July Fi 
ih > ee 21 30 11 Left 2 5 4 0 0 6.0 7 4 0 0 
July 
TYAS 2, wis 22 30 4 Left 22 0 2 0 1 34.0 | 8 9 3 4 
July 
T/Nadis occu 21 30 61 Left 56 1 4 5 18 12 17 2 30 
July 
T/18-p... 2.0 16 30 17 Left 17 0 0 0 1 38.0 2 4 1 0 
July 
7/16-e....... 16 30 15 Left 15 0 0 0 0 38.2 0 9 0 6 
July 
1/15-2..... 15 30 21 Left 20 0 1 0 1 33.5 1 20 0 0 
16 30 27 Left 7 8 2 0 0 20.9 16 2 6 
Wee ted 30 56 Left at v o a 28 3 8 6 39 
7/16-a aoe ve 30 3 Left AON a2 d ¥ 0 g8 | 2B 0 | 10 
10/8-Big. aoe et: 20-78 25 Right 25 0 0 1 3 68.0 0 8 5 12 
[An St... 
Total Lee 3077 2699 207 Wi | 477 204 287 | 1619 493 678 














REACTIONS TO LIGHT IN VANESSA ANTIOPA 381 


said to have oriented in the ‘shaded region.’ When orientation 
occurred either precisely at the edge of the beam or within one 
centimeter beyond the edge it is considered to have occurred 
‘near the edge of the beam.’ In those trials in which the insect 
either continued to perform circus movements or passed on out- 
side the beam into the shaded region beyond, in a more or less 
straight course with no turn toward the source of light, ‘no 
orientation’ is said to have occurred. 

An examination of this table shows that out of a total of 3077 
trials the butterflies turned toward the functional eye in 2699 
trials, and away from it in 207 trials, while in 171 trials they 





Fig. 7 Reproduction of 33 successive trails made by butterfly 10/14-b (left 
eye blackened) on the first day of the tests. a and b, limits of horizontal beam 
of light; 1-33, paths made in successive trials; small arrows, direction of move- 
ment of animal; large arrows, direction of rays of light; illumination at z, 1510 
mec.; at y, 250 mc. Note that this insect modified its behavior in that it per- 
formed circus movements in 13 out of the first 16 trials, but made circus move- 
ments in only 6 of the next 16 trials. 


moved toward the glower without first turning toward one side 
or the other. This indicates clearly that there is in Vanessa 
with one eye blinded a strong tendency to turn toward the func- 
tional eye. 

The table shows aiso that in 2399 of the 3077 trials individuals 
with but one functional eye oriented and moved fairly directly 
toward the light, and that in 287 trials orientation occurred in 
the beam of light, indicating strongly that both eyes are not 
necessary in this process. 


382 WILLIAM L. DOLLEY, JR. 


It shows, moreover, that in 16 of the 27 individuals tested on 
more than one day orientation occurred in more trials of the last 
day than in those of the first, and that in 18 of the 27 individuals 
orientation at the edge of the beam occurred more promptly 
during the trials on the last day than it did during those on the 
first. This is well illustrated by the reactions of butterfly 
10/25-a, described in table 1 and in figures 2, 3, and 4. 

It shows, furthermore, that in 20 of the 27 individuals circus 
movements decreased in number, and that in 20 the average 
. angle of deflection was less in the trials of the last day than it, 
was in those of the first. Although not shown in table 1, 10 indi- 
viduals performed fewer circus movements in the last trials of 
the first day of the tests than in the first trials on this day. 

This seems to indicate clearly that with practice there is in 
Vanessa with but one functional eye improvement in the accuracy 
of orientation in three respects, as previously stated: (a) increase 
in promptness of orientation, (b) decrease in the number of circus 
movements performed, and (c) decrease in the angle of deflection. 

If this is true, then it is evident that orientation is not depend- 
ent upon the stimulation of both retinas by equal amounts of light 
energy. This conclusion is strongly supported by the fact that 
in 171 out of 3077 trials the organism with but one functional eye 
did not turn either to the right or the left, but moved fairly 
directly toward the source of light. It is moreover supported 
by the results obtained in observations on: the relation between 
the degree of curvature in circus movements and the luminous 
intensity, relation between the angle of deflection and the lumin- 
ous intensity, and reorientation after changing the direction of 
the beam of light. These are discussed in the following para- 
graphs. 


2. Relation between the degree of curvature in circus movements 
and the luminous intensity 


According to the ‘continuous action theory’ smaller curves 
should be made in the strong light in the beam than are made in 
the weak light outside the beam, for the adherents of this theory, ~ 
as stated above, hold that the tension of the muscles of the legs 


REACTIONS TO LIGHT IN VANESSA ANTIOPA 383 


on the two sides of the body varies with the relative amount of 
light energy received by the two retinas. No such relation, 
however, was at all evident in the observations on Vanessa. 
Curves of the same size were made in both positions, and very 
frequently those in the region of low illumination outside the 
beam were smaller than those in the region of comparatively 
high illumination in the beam. This is well seen in the ninth 
trial made by animal 10/14-b on the third day (fig. 8). In this 
case the butterfly, while in the beam, began to perform a circus 
movement of a diameter of 6.5 cm. By the time it was half 





Fig. 8 Reproduction of 21 successive trails made by butterfly 10/14-b (left 
eye blackened) on the third day of the tests. a and b, limits of horizontal beam 
of light; 1-21, paths made in successive trials; small arrows, direction of move- 
ment of animal; large arrows, direction of rays of light; illumination at x, 1510 
mc.; at y,250mc. Note that in trial 9 this insect turned very much more sharply 
toward the functional eye while in the shaded region to the right of the beam than 
it did while in the comparatively strong light in the beam. 


completed the animal was 3 cm. beyond the edge, and in the 
weak light to the right of it. On reaching this point, the insect 
turned sharply to the right, and made another circus movement 
of a diameter of only 1.5 cm. ie., in weak light the organism 
turned more sharply toward the functional eye than in strong. 
Similar reactions were observed in many other cases. 


3. Relation between the angle of deflection and the luminous intensity 


a. Effect of beginning the trials in different intensities. It has 
been shown that in those trials before the Nernst glower in which 
circus movements are not performed continually, Vanessa antiopa 


384 WILLIAM L. DOLLEY, JR. 


usually turns until it assumes a certain angle with the rays of 
light, and that it then proceeds diagonally across the beam. If 
orientation is dependent upon the relative amount of light energy 
received by the two eyes, as demanded by the ‘continuous action 
theory,’ the degree of deflection ought to be greater in high 
illumination than in low, for if only one eye is functional, the 
greater the intensity, the greater the difference in the amount 
of energy received by the two eyes. This was tested by measur- 
ing the angles of deflection in different intensities of light in each 
one of the trials made by all of the insects. The results of some 
of these tests are recorded in figure 9 and in table 2. 


TABLE 2 


Angles of deflection made in different intensities of light by four butterflies with one 
eye blackened 





5 BUTTERFLY 9/22-a BUTTERFLY 10/1-3-b BUTTERFLY 10/8-a BUTTERFLY 10/1-4-b 
B | egee jal ees i |eere | 2 7 eeeeue 
e\ScF_| 3 |Se28_| = |Sect.| = |Sec8.| § 
sped OH od q Ok wo q OR ah Og a 
Be Bs aee| #3 | $2 EE EE oe EE gs S525 P| #3 
1 380 50 257 80 234 85 234 50 
2 380 85 383 80 445 110 275 30 
3 624 50 758 50 445 90 624 55 
4 2153 60 758 70 624 85 234 30 
5 380 95 ‘791 40 275 80 234 30 
6 448 65 936 50 791 70 634 50 
7 624 50 234 40 383 70 634 50 
8 1223 50 337 40 1044 70 936 95 
9 2153 65 624 35 218 50 257 90 
10 380 75 936 50 234 85 337 90 
11 448 80 257 50 257 85 416 75 
12 624 60 314 60 634 70 234 100 
13 839 65 416 60 291 70 337 80 
14 1497 55 624 50 1044 70 624 85 
15 2883 80 936 45 416 60 936 _ 110 
16 380 65 257 65 234 60 
17 547 80 337 45 624 50 
18 624 75 624 35 259 60 
19 711 80 257 110 1044 50 


REACTIONS TO LIGHT IN VANESSA ANTIOPA 385 


By referring to this figure, which represents the course of a 
given individual in different intensities of light it will be seen 
that the angle of deflection is essentially the same in all, in spite 
of the fact that the illumination varied from 76 to 3397 me. 
This is a typical case. It seems to show that the degree of 
deflection is within wide limits independent of the intensity of 
the light. 





Fig. 9 Diagram showing the angles of deflection made by butterfly 10/8-b 
(left eye blackened) when exposed in light of different intensities. A A, limits 
of horizontal beam of light; 14-25, successive trials; 76 and 3397, intensity of light 
in meter candles at the corresponding points. Note that the insect deflects at 
about the same angle with the rays of light, no matter whether the trials are 
begun in an intensity of 76 me. or in an intensity of 3397 mc. 


The results presented in table 2 support this contention. They 
demonstrate that, while the degree of deflection varies greatly 
in different individuals and in the same individual under different 
conditions, there is no apparent correlation between it and the 
intensity of the light. Since the degree of deflection is a measure 
of the difference in tension of the muscles of the legs on the two 
sides of the body these results also show that there is no apparent 
correlation between this difference in tension and the intensity 


386 WILLIAM L. DOLLEY, JR. 


of the ight. This conclusion receives still further support from 
the results obtained in non-directive light which are reserved for 
discussion later. Before entering upon further discussion based 
on table 2 we will describe experiments as to the effect upon 
behavior of changes of intensity. 

b. Effect of sudden changes of intensity on the ek of deflection. 
The previous experiment in which the position of the glower was | 
unchanged, but in which the intensity of the light varied in 
different trials was supplemented by others. In some of these 
the light was increased after the butterflies had oriented. In 
others it was suddenly decreased. The insects with only one 
eye functional were placed in a beam of light, and, as soon as 

TABLE 3 


Effect upon the angle of deflection of suddenly increasing the illumination from 104 
mc. to 1400 mc. 


NUMBER OF NUMBER OF NUMBER OF 





DESIGNATION OF TRIALS IN WHICH TRIALS IN WHICH TRIALS IN WHICH 
BUTTERFLIES ANGLES WERE ANGLES WERE NO EFFECT WAS 
INCREASED DECREASED EVIDENT 
10/2021 <a. 4) eee 5 
LOVG=9=b', vanced eae Cee s 2 8 
LOU S= Cian isc co ae ee eee 8 1 3 
10/3 =0-8) o)..e ee 1 1 
LO f=7<c ls. eee eee 5 3 
otal... 21 4 15 








they had assumed a definite direction of locomotion, the glower 
was suddenly moved closer to the organisms, or was suddenly 
moved further away. In this way the intensity of the light was 
suddenly changed from 104 me. to 1400 me. and vice versa. 
Some butterflies turned suddenly toward the functional eye, 
others turned toward the blinded eye, and still others did not 
respond. The reactions of the animals to sudden increase of 
intensity are given in table 3; those to a sudden decrease of 
intensity in table 4. 

Table 3 shows that in 21 out of 41 trials, the insects nme 
ately turned toward the functional eye when the light was sud- 
denly increased; that in 4 they turned toward the blinded side; 
and that in 15 there was no response. 


REACTIONS TO LIGHT IN VANESSA ANTIOPA 387 


Table 4 shows that four butterflies were tested, making 23 
trials in all, and that in 12 of these there was no response, while 
in 8 the butterflies turned toward the blackened eye, and in 3 
toward the functional eye. 

The results recorded in these two tables show clearly that a 
sudden increase of intensity tends to cause the butterflies to turn 
sharply toward the functional eye and that a sudden decrease 
tends to cause them to turn in the opposite direction. 

The reactions, as described above, upon a sudden change in 
the intensity of the light are very puzzling until the behavior of 
the individual animals is carefully examined. In one of the 
butterflies, 10/8-c, whose reactions are given in table 3 and in 


TABLE 4 


Effect upon the angle of deflection of suddenly decreasing the illumination from 1400 
mc. to 104 mc. 








NUMBER OF NUMBER OF NUMBER OF 
DESIGNATION OF TRIALS IN WHICH TRIALS IN WHICH TRIALS IN WHICH 
BUTTERFLY ANGLES WERE ANGLES WERE THERE WAS 
INCREASED DECREASED NO APPARENT EFFECT 
1 4 4 
1 2 
2 
1 + 
+ 2 
3 | 8 12 








figure 10, the angle of deflection did not change in three trials, 
but in seven out of the other nine trials made, it increased, at 
once, when the intensity was suddenly increased. Immediately 
afterwards, however, as shown in figure 10, the organism turned 
toward the glower, and deflected at a smaller angle with the rays of 
light than it hud before the intensity had been increased. In one 
trial, though, at the sudden increase of intensity, it decreased 
the angle, and deflected only slightly in the bean. In another 
trial it increased the angle and went out of the beam. ° 

The behavior of this last animal gives, I think, the clue to 
the explanation of the fact that when the intensity of the light is 
suddenly changed the angle of deflection decreases in some ani- 
mals, while in others it increases. The fact that this butterfly 


388 WILLIAM L. DOLLEY, JR. 


(fig. 10) increased the angle of deflection at the sudden change 
of intensity, and then immediately decreased the angle of deflection, 
although the insect was closer to the glower, is very significant 
in showing that it is not the higher intensity which caused the 
increase in the angle of deflection, but that it is the sudden change 
from a lower to a higher intensity. Consequently, the sudden 
increase in the angle of deflection that occurs in some cases, seems 


A 





A\ cl bb *oiB Bl bl le ‘lie mle iF f 





“ay y ( 
A i 


gt [ASle# mal high nat Wills Ji 5! letgi« Kiel Mo 4in Lb 











t 


Fig. 10 Semi-diagrammatic reproduction of the records made by butterfly 
10/8-c (left eye blackened) when the illumination was suddenly increased from 
104 mc. to 1400 mc. The individual trials are numbered. The limits of the 
beams of high intensity are designated by the capital letters; the beams of low 
intensity by the small letters. X, position of the animal at the time the illumi- 
nation was changed; arrows, direction of movement of animal. Note that the 
insect usually turned sharply toward the functional eye immediately after the 
illumination was increased, and later again in the opposite direction. 


to be a shock reaction and not the result of unequal amounts 
of light energy received by the two retinas, as is demanded by 
the ‘continuous action theory’ of orientation. Furthermore, 
according to this theory the angle of deflection should be-greater 
in high than in low intensity. This was, however, not found to 
be true, as is shown in table 2 and figure 9. By referring to this 
table it will be seen that the angle of deflection in 2000 me. 
and in 200 me. was essentially the same, whereas, according to 


REACTIONS TO LIGHT IN VANESSA ANTIOPA 389 


the ‘continuous action theory’ it should be ten times greater in 
the former intensity than in the latter. Moreover, this theory 
is not supported by the results obtained when the illumination 
is gradually increased after the animals have become oriented in 
a beam of light. The condition mentioned is fulfilled in the 
experiments already described in which the insects with one 
functional eye were tested in a beam from a stationary glower. 
In figures 4 and 9 it can be seen that after the butterflies had 
become oriented and were moving toward the source of light 
at a definite angle with the rays they were gradually approaching 
the glower and consequently the illumination was at the same 
time being gradually increased. On the basis of the ‘continuous 
action theory,’ one would expect the butterflies while in the beam 
to curve gradually toward the functional eye, increasing the angle 
of curvature as they approached the glower. On the contrary, 
they moved while in the beam in fairly straight courses, and the 
angle of deflection remained practically unchanged as the organ- 
isms drew nearer to the source of light. 

This work shows conclusively that the angle of deflection does 
not vary with the intensity of the light, thus indicating most 
strongly that orientation in Vanessa is not necessarily dependent 
upon the relative amounts of light energy received by the retinas. 
It also seems to show that the assumption that the tension of 
the muscles controlled by the two retinas varies with the amount 
of light energy received, does not hold. This conclusion is further 
supported by the fact that Vanessa with only one eye functional 
can reorient toward either side and so follow a source of light 
as its position is changed, as is shown in the following section. 


4. Reorientation after changing the direction of the beam of light 


To ascertain whether or not butterflies with but one func- 
tional eye can reorient they were placed into a horizontal beam of 
light and after they had assumed a definite axial position and were 
moving toward the source of light at a definite angle to the direc- 
tion of the rays, as previously described, the source was moved _ 
to a second position at the same distance from the animal, but 


390 WILLIAM L. DOLLEY, JR. 


such that the rays of light were now at right angles to their 
former direction. When this was done, it was found that the 
butterflies usually reoriented. That is, they usually turned until 
they again assumed the same axial position with reference to the 
direction of the rays of light that they had taken before the glower 
was moved. This occurred no matter if the glower was moved 
to the right or to the left. Thus, it is evident that in the process 
of reorientation the animals may turn either toward the blinded 
or the functional eye (figs. 11 and 12). 

Thirty-one butterflies were used in this experiment, and it 
was found that, of these, twenty-two reoriented both to the right 
and to the left. Nine, however, although they reoriented toward 
the functional eye, did not turn toward the blackened eye. 
Three of these were kept and tested for several successive days. 
The behavior shown in these tests is recorded in table 5. 

These results show clearly that Vanessa with only one eye 
functional can reorient, and in this process can turn either toward 
the blinded eye or toward the functional eye. They also show 
that the behavior may become modified since those insects that 
do not reorient by turning toward the blinded eye when first 
tested are able to do so after a certain amount of experience 
(fig. 12, 1-3). Moreover they seem to support the conclusion 
derived from results described previously that the performance 
of circus movements seems to be favored by a sudden change in 
light conditions, since in four of the trials described in table 6 
the butterflies either performed circus movements, or apparently 
began to perform them, when the position of the glower was 
suddenly changed. 

The ability of the butterflies with only one eye functioning to 
reorient, and so follow the source of light as its position is changed 
is important in a consideration of the factors in the process of 
orientation. It has a direct bearing on whether or not orienta- 
tion in light is dependent upon stimulation of symmetrically 
located photosensitive areas, as demanded by Loeb’s theory of 
orientation. In reorientation, such as has been described, only 
one retina is affected by light. The chemical changes taking 
place in the two photosensitive areas are not at all identical. 


REACTIONS TO LIGHT IN VANESSA ANTIOPA 


TABLE 5 


391 


Behavior of three butterflies tested for reorientation on several successive days 


DESIGNATION| OF DAYS |NUMERICAL 


OF 
BUTTERFLIES 





10/21-b.... 





NU MERICAL 


ORDER 


ON WhICH 


TESTS 
WERE 
GIVEN, 


1 


bo 





BEHAVIOR WHEN GLOWER 








BEHAVIOR WHEN GLOWER 




















ORDER WAS MOVED TO THE SIDE OF | WAS MOVED TO THE SIDE OF 
OF TRIALS THE COVERED EYE THE FUNCTIONAL EYE 
1 Circus movement toward | Reoriented 
functional! eye, followed by 
movement toward glower 
, Circus movement ] Reoriented (See fig. 12, 4) 
toward functional 
eye, followed by 
movement toward 
glowe1 See fig- 
2 Circus movement } ure12,| Reoriented 
toward functional 1-3 
eye, followed by 
movement toward 
glower 
3 Reoriented J Reoriented 
1 Failed to reorient Reoriented 
2 Failed to reorient Reoriented 
=) Reoriented Reoriented 
4 Reoriented Reoriented 
1 Reoriented Reoriented 
2 Reoriented Reoriented 
1 Failed to reorient Reoriented 
2 Failed to reorient Reoriented 
3 Failed to reorient Reoriented 
4 Failed to reorient Reoriented 
5 Failed to reorient Reoriented 
6 Reoriented Reoriented 
1 Reoriented Reoriented 
1 Reoriented Reoriented; immediately per- 
formed circus movement to- 
ward functional eye; then 
went toward glower 
1 Reoriented Reoriented 
1 Circus movement toward | Reoriented 


10/24-a.... 4 














functional eye, followed by 
movement toward glower 


Sharp turn toward functional 
eye as if to make circus, but 
turned and moved toward 
glower 





Behavior similar to that shown 
when glower was moved to 
side of covered eye 





392 WILLIAM L. DOLLEY, JR. 


The organism is non-symmetrical, only one eye being functional. 
And yet the butterfly moves toward a source of light, deflecting, 
it is true, toward the functional eye, and when the position of 
the light is changed, the animal also changes the direction of its 
motion to correspond with the change in position of the source 
of light. This behavior bears little resemblance to that which 
would be exhibited were the organism such that it could only 





Fig. 11 Reproduction of trails made by four butterflies showing reorientation. 
Large arrows, A and B, direction of rays of light in the two positions of the 
glower; small arrows, direction of movement of the butterflies; x, position of 
animals when the direction of the rays was changed; 1 and 2, trails made by butter- 
fly 7/29-d; (left eye blackened); 3 and 4, trails made by butterfly 7/16-c (left eye 
blackened); 5 and 6, trails made by butterfly 7/29-b (left eye blackened); 7 and 
8, trails made by butterfly 9/22-b (right eye blackened). 


REACTIONS TO LIGHT IN VANESSA ANTIOPA 399 


results secured by Hadley with larval lobsters. He found that 
these animals, at all ages, moved in circles toward the blinded eye, 
although they vary in the sign of their reaction to light at differ- 
ent ages. He says (08, p. 197): ‘‘In the lobster larvae all the 
progressive reactions which took place immediately following the 
blinding of one eye were positive. In certain cases it appeared 
that either the operation itself, or the effects of blinding changed 
the index of reaction from negative to positive. In all these 
instances, whether the previous reaction had been negative or 
positive, the resulting behavior was the same; a series of revo- 
lutions, or circus movements, or a progression in which the direc- 
tion of turning indicated that the influence of light on the 
unblackened eye was to cause greater activity of the swimming 
appendages on that side of the body, while blinding invariably 
had the opposite effect. In other words, the reaction of. the 
blinded positively reacting lobster larvae corresponds with those 
of Holmes’s negatively reacting amphipod, Hyalella dentata 
(Smith) but not with his positively reacting amphipods.” 
Hadley is the only investigator who records continuous move- 
ments only toward the non-functional eye in individuals both in 
the positive and in the negative state. It is therefore probable 
that the circus movements described by him were due not to the 
withdrawal of the light stimulus from one eye, but to the stimu- 
lation produced by searing the eye with a hot needle, which was 
the method used by him in blinding his animals. These experi- 
ments ought to be repeated and the organisms tested on succeed- 
ing days. Besides, this method of blinding the lobster should 
be supplemented by entirely cutting off the eye stalk and testing 
for several days in succession the young lobsters so operated on, 
‘thus eliminating the possible effect of injury on the response. 


D. BEHAVIOR IN NON-DIRECTIVE LIGHT 


In the preceding pages we have discussed the behavior of 
Vanessa in a horizontal beam of light, and in the absence of light. 
We shall now describe its reactions in a field uniformly illumi- 
nated from above. When the butterflies are placed in a beam 
of light, all of the light that reaches them emanates practically 


400 WILLIAM L. DOLLEY, JR. 


from one point, so that the illumination of the functional eye 
varies with every change in position of the animals. The ques- 
tion naturally arises as to whether or not many of the reactions 
observed under these conditions are due to this change in the 
illumination. This was settled conclusively by placing the butter- 
flies with one eye blackened in light so arranged that the illumi- 
nation of all of the large portions of the uncovered eye was 
essentially the same in all of the positions assumed by the insects, 
i.e., in which the light was non-directive. 

To accomplish this the box described in the preceding section 
was used. Over the top of the box there was drawn an opaque 
cloth cover, in the center of which a circular hole, 3 cm. in 
diameter, was cut. A 16 ¢.p. electric lamp was placed directly 
over this hole in contact with the cloth. The butterfly was then 


Fig. 16 Reproduction of trail in non-directive light, 6 mc., made by butterfly 
7/16-c (right eye blackened) immediately after the eye was covered. Note the 
continuous turning toward the functional eye. 


placed upon the papers in the bottom of the enclosure. Some 
light was reflected from the sides and bottom of the black box, 
but the amount of this reflected light was comparatively very 
small, and, moreover, it was approximately equal on all sides of 
the animal. The luminous intensity at the bottom of the box 
was 6 me. ; 

Thirty-one butterflies were tested in this apparatus in non- 
directive light soon after one eye had been blackened, and nine 
were also given trials on several successive days. The behavior 
exhibited by these animals is recorded in figures 16 and 17 and 
in table 6. 

A study of this table and the figures show that if Vanessa 
antiopa with one eye blackened is placed in non-directive light 
it tends to turn continuously toward the functional eye, and that 


REACTIONS TO LIGHT IN VANESSA ANTIOPA 397 


to the contact stimulus exerted by the covering of the blackened 
eye, for in light the insects turn toward the functional eye. It 
seems to demonstrate, moreover, that there is but little, if any, 
permanent modification in the behavior on successive days, for 
essentially similar reactions were observed in all of the insects 
during the whole period over which the tests extended. 





Fig. 15 Reproduction of trails in total darkness made by butterfly 7/11 (right 
eye blackened) in ten successive trials forty-eight hours after the eye had been 
covered. Compare the preceding figure with this one, and note that in the tests 
on three successive days this butterfly usually turned continuously toward the 
blackened eye, showing little, if any, modification in behavior. 


The results obtained in these experiments throw light on the 
puzzling results which Holmes and McGraw obtained in their 
experiments with butterflies. They used a jar, the bottom and 
sides of which were lined with white paper. This was covered 
by a cone of the same material, and at the apex of this cone, 
an electric light was placed. When butterflies with one eye 


398 WILLIAM L. DOLLEY, JR. 


blackened were placed in the center of the enclosure, specimens 
of some species went uniformly in circles toward the uncovered 
eye, while those of other species, among them Vanessa antiopa, 
moved continuously toward the blinded eye, although all were 
positive. Since insects which are positive in their reactions to 
light usually go in circles toward the uncovered eye, when one 
eye is blackened, while those which are negative go in circles 
toward the blackened eye, the above results were apparently 
inexplicable. Since, however, Vanessa antiopa, which is highly 
positive, goes in darkness in circles toward the blinded eye, it 
is clear that the results secured by Holmes and McGraw are to 
be explained by the fact that at times the stimulus exerted by the 
covering of the eye was strong enough to overcome the stimulus 
exerted by light on the uncovered eye. When the butterflies went 
toward the functioning eye, they were responding to light, while 
when they went in circles toward the blinded eye they were re- 
sponding to the stimulus exerted by the covering of the blackened 
eye. 
The above statement probably applies equally well to the 
peculiar results which Brundin obtained. These are described 
in the following.manner (13). 

“Tn positive specimens of Orchestia traskiana, circus move- 
ments will occur as often toward the blackened eye as toward 
the normal eye. All specimens used for this experiment were 
strongly positive. There is no way to account for this varia- 
bility, except that the animal might be made temporarily nega- 
tive by having one of the eyes covered over. The fact, however, 
that as soon as the blackening is removed from the eye of one 
of these ‘apparently negative’ specimens, its reactions to the 
light is decidedly positive, seems to throw considerable doubt 
upon this hypothesis.” 

It seems very probable that the circus movements toward the 
blackened eye performed by this amphipod were due to a stimulus 
produced by the covering of the blinded eye and were not due 
to light. 

It is possible, also, that the above described behavior in dark- 
ness of Vanessa may be suggestive in connection with the peculiar 


REACTIONS TO LIGHT IN VANESSA ANTIOPA 395 


This general statement of the behavior is illustrated by the 
following detailed description of the reactions of two insects. 

1. Butterfly 7/16-c (right eye blackened) was tested in dark- 
ness ten hours after the eye had been covered. It moved con- 
tinually toward the blinded eye (fig. 13). 

2. Butterfly 7/11 (right eye blackened) was tested immedi- 
ately after the eye had been covered and again on each of the 
following two days. In the first trial it turned continuously 
toward the blackened eye. In the second and third it went in 
straighter courses, but showed a decided tendency to curve to 


Fig. 13 Reproduction of tracings made in total darkness by butterfly 7/16-c 
(right eye blackened) showing continuous turning toward the blackened eye. 
Arrows indicate direction of movement. This record was made ten hours after 
the eye was covered. 


the right (fig. 14, A). On the second day three trials also were 
given, and in each of these the organism turned continuously 
toward the blackened eye (fig. 14, B). On the third day in the 
first five of the ten trials given this insect again turned continu- 
ously toward the blinded eye, and in. the other five it deflected 
in the same direction, but not so strongly as in the first five 
trials (fig. 15). It can thus be seen that the behavior exhibited 
on the first day was, in general, retained on the succeeding days 
of the tests. 

- Similar results were obtained in observations on a number of 
other specimens. These may be summarized as follows: Eight 
butterflies were tested for ten minutes each day for ten consecu- 


396 WILLIAM L. DOLLEY, JR. 


tive days; three for four days; three for three days; one for two 
days; and thirteen on only one day. All of these animals usually 
turned continuously toward the blackened eye.’ The behavior 
was strikingly uniform. This continuous movement toward the 





Fig. 14 Reproduction of trails made by butterfly 7/11 in total darkness (right 
eye blackened). A, 1-3, trails made in three successive trials immediately after 
the eye had been covered. B, 1-3, trails made in three successive trials twenty- 
four hours later. 


blackened eye under conditions in which no light can affect the 
uncovered eye shows conclusively that the covering of the eye 
exerts a stimulus of some sort upon the organism. It also shows 
that the deflection toward the functional eye in light is not due 


REACTIONS TO LIGHT IN VANESSA ANTIOPA 393 


orient if both eyes were stimulated equally. Were this hypothe- 
sis true, the animal with only one eye functional could not orient, 





Fig. 12 Reproduction of trails made by three butterflies showing reorienta- 
tion. Large arrows, A and B,-direction of rays of light in the two positions of 
the glower; small arrows, direction of movement of the butterflies; x, position of 
the animals when the direction of the rays was changed; 1-4, trails made by butter- 
fly 7/4 (right eye blackened) ; 5-6, trails made by butterfly 10/21-b (left eye black- 
ened); 7-8, trails made by butterfly 10/24-a (right eye blackened). Note that 
butterfly 7/4 (right eye blackened) failed to reorient promptly toward the side 
of the blackened eye in the first two trials, but that in the third it did reorient 
promptly in this direction, showing marked modification in behavior. This figure 
and the preceding one are presented not merely to show the accuracy with which 
Vanessa, with only one eye functional, reorients upon change in position of the 
source of light, but also to show some of the peculiarities exhibited by different 
individuals. 


THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 20, No. 3 


394 WILLIAM L. DOLLEY, JR. 


but would be compelled to perform circus movements continu- 
ally, regardless of the position of the source of light. 

This experiment, however, throws no light on the nature of 
the stimulus effective in orientation. Reorientation could con- 
ceivably occur in organisms with but one functional eye, whether 
light exerts its orienting stimulus through its continuous action, 
as demanded by the ‘continuous action theory,’ or througha 
change of intensity, as demanded by the ‘change of intensity 
theory.’ ; 


C. EFFECT OF THE COVERING OF THE EYE OWING TO CONTACT 


We have clearly demonstrated that Vanessa with but one 
functional eye tends to turn toward this eye when it is placed 
in a beam of light, and that this tendency decreases with experi- 
ence. Are these responses due to the elimination of the action 
of light on the blinded eye or to the effect of the contact of the 
covering on this eye? This question was answered very con- 
clusively by placing in darkness specimens with one eye covered. 
In this experiment a wooden box (45 x 55 x 59 cm.) lined with 
black cloth was used. In the bottom of this box were placed 
sheets of paper covered with soot. The butterfly to be tested 
was placed in the enclosure upon the sheets of paper, and an 
opaque cover was drawn over the top of the apparatus. All the 
experiments were performed in the dark room, many of them 
late at night. The precautions taken were of such a nature that - 
the observer feels confident that no light could possibly have 
reached the organisms. 

Under these conditions it was found that the animals made 
circus movements, but in the reverse direction from that in 
which they moved in the presence of light. With few exceptions, 
the butterflies turned continuously toward the blinded eye, and in 
most of the exceptional cases they showed a decided tendency to 
curve somewhat in this direction. Only in a few cases did they 
move in a straight line. In some of these the course was nearly 
straight for eight or ten centimeters or more. 


TABLE 7 


Showing the relative degree of curvature between the circus movements made in non- 
directive light of low intensity and those made in that of high intensity 





407 


(a paeerieae NON-DIRECTIVE LIGHT OF AN NON-DIRECTIVE LIGHT OF AN 

BUTTERFLIES INTENSITY OF 2 MC, INTENSITY OF 460 mc. 

9/22-c Circus movements Fairly straight courses with a de- 
cided curve toward uncovered 
eye 

9/22-b Circus movements Circus movements with larger 
angles of curvature 

9/21-a Circus movements Circus movements with slightly 

larger angles of curvature 

9/22-d Similar circus movements 

10/1-a Circus movements Circus movements with much 
larger angles of curvature 
10/1-b Fairly straight courses although | Fairly straight courses with nu- 
circus movements are made merous turns toward the black- 
ened eye 
10/1-c Fairly straight courses in fifteen | Fairly straight courses in fifteen 
trials trials 
Under both conditions a decided tendency to turn toward the func- 
tional eye though numerous turns are made toward the black- 
ened eye 
10/1-c-6 Circus movements in both cases—records indistinguishable 
10/13-a Circus movements Circus movements with much 
larger angles of curvature 
10/14-18-a | Fairly straight courses under both conditions 
10/16-a Trials indistinguishable 
10/20-a Circus movements Circus movements with much 
larger angles of curvature 
10/21-b Circus movements: Circus movements with slightly 
larger angles of curvature 
10/24-a Circus movements Circus movements with slightly 
larger angles of curvature 
* 10/28-a Circus movements in both cases—records indistinguishable 
10/31-a Circus movements Straightened courses 


408 WILLIAM L. DOLLEY, JR. 


fairly straight courses with a decided curve toward the uncovered 
eye. In the case of seven individuals the trials made in the two 
conditions of illumination were indistinguishable. 

In table 8 are given the results obtained when non-directive 
light of a very low intensity was used. 


TABLE 8 


Amount of decrease in intensity of non-directive light necessary to force the bulter- 
flies to cease making circus movements toward the functional eye and to make 
circus movements in the-opposite direction 





ESE es THE DIRECTION OF THE Ce tee as eae CIRCLES TOWARD THE 
UNCOVERED EYE BLINDED BYE 
0.24 me. 0.09 me. 0.0265 me. 
23 0.15 me 0.1 me. 0.265 me. 
0.043 me. 
3 0.52 me. 0.4 me. 0.18 me. 
0.273 me. 
4 0.114 me. 0.47 me. 
0.036 me. 0.025 me. 
ix 0.077 me. 0.046 me. 
0.014 me. 0.011 me. 











This table shows, in general, that the animals placed in non- 
directive light of low intensity, half a meter-candle or less, make 
circus movements toward the functional eye; that if the inten- 
sity of the light is then decreased, the insects deflect less and 
less until their courses become relatively straight; and that if 
the intensity is then still further decreased, they move in ‘circles’ 
‘toward the blackened eye. 

It must be concluded from these reactions that it is probably 
true that in light below certain limits, the effect of*the light 
and that of the covering of the eye, may become equal. But, if 
this is true, it does not necessarily mean that the nature of the 
stimulus produced by the contact of the covering with the eye 
and that caused by light in the opposite eye is the same. It is 
possible that while the covering probably stimulates through its — 
continuous action, light may stimulate by virtue of change of 
intensity. ‘This may well be so, and yet the effect of the two 


REACTIONS TO LIGHT IN VANESSA ANTIOPA 405 


light was reduced to 2 me. The higher intensity was produced 
by replacing the 16 c.p. lamp with two Nernst filaments side by 
side. The luminous intensity produced in this way was 460 
me. ‘The insects were tested first in the light of low intensity, 
and then in that of high intensity. They were kept in darkness 
for twenty minutes before being exposed to either of these two 
lights. In the second experiment a white sheet of paper measur- 
ing 20x 17 cm. fastened over a piece of board of the same size, 
was placed above the center of the box at an angle of forty-five 
degrees with the plane of the bottom. A horizontal beam of 
light from a Nernst glower was thrown on this sheet of paper, 
and reflected into the box below. By altering the elevation of 
the reflecting surface, and also by varying the distance between 
the glower and this surface, the intensity of the light in the box 
could be changed. In this way light of very low intensity was 
produced. 

The results obtained in these experiments may be illustrated 
by a description of the behavior of two animals. 

Butterfly, 10/13-a (left eye blackened), after having been in 
darkness twenty minutes, was exposed to non-directive light of 
an intensity of 2 me. It made four circus movements, turning 
continuously toward the functional eye, and then stopped. It 
was picked up and dropped a second time, on the smoked papers 
in the bottom of the box. In this, the second trial, it again per- 
formed circus movements in the same direction. Similar reac- 
tions were observed in all the rest of the ten trials made (fig. 18). 
After a stay of twenty minutes in darkness, the source of light 
of high intensity was used, and the insect was given ten trials. 
In all of these it either made circus movements in the same direc- 
tion as in the lower intensity, with a much smaller degree of 
curvature, or walked in fairly straight courses, as is shown in 
figure 19. 

Instead of moving in smaller ‘circles’ in light of high intensity 
than in that of low intensity, as the ‘continuous action theory’ 
demands, the organism showed the reverse behavior, for the 
smaller ‘circles’ were all made in the lower intensity instead of in 
the higher. ; 


406 WILLIAM L. DOLLEY, JR. 


Butterfly 10/3-a (right eye blackened) was placed in non- 
directive light of very low intensity, and this intensity was then 
still further decreased. It was found that circus movements 
toward the functional eye continued to be performed until the 
intensity reached 0.24 me. When it was, however, still further 
decreased, the courses became more and more direct, until at 0.09 
me. the animal moved in a fairly straight line. When the in- 
tensity was lowered still further the butterfly deflected toward 
the blackened eye, and when it had reached 0.0265 me. the insect 
moved in ‘circles,’ turning toward this eye. 





Fig. 18 Reproduction of trails made in non-directive light of low intensity, 
2 mce., by butterfly 10/13-a (left eye blackened). Note that the animal moves in 
small ‘circles’ continuously toward the functional eye. 


The reactions described above are typical of those exhibited 
by the twenty-one butterflies exposed to non-directive light of 
different intensities, as is shown in tables 7 and 8. 

From table 7 it can be seen that out of sixteen animals tested 
in non-directive illumination of two intensities, one 230 times 
greater than the other, in not a single case did an animal move 
in smaller ‘circles’ in the higher than in the lower intensity. On 
the contrary, four butterflies actually made much smaller ‘circles’ 
in the weak light than they did in the strong light, and three 
animals made slightly smaller ‘circles’ in the weaker light. More- 
over, one insect which made circus movements in the weaker 
light did not make any at all in the stronger, but rather went in 


REACTIONS TO LIGHT IN VANESSA ANTIOPA 403 


eye was functional. But when placed in non-directive light, 
essentially the same surface of the functional eye was continu- 
ously illuminated; while in a horizontal beam, the surface of the 
eye illuminated changed whenever the animal turned in either 
direction. The absence of circus movements in the beam of 
light must, therefore, have been due in some way to the change 
in the illumination of different regions of the eye, produced by 
the lateral movements. 

This conclusion is further supported by the fact that all of the 
animals with one eye blackened used in the experiments de- 
scribed in the present paper, if placed before a window per- 
formed circus movements continuously, whenever they moved. 
In some cases the organisms were kept under these conditions 
for as long as two weeks, and frequent observations revealed no 
modification in their behavior. Yet when these same insects 
were placed in a horizontal beam from a glower they made no 
circus movements after a certain amount of experience. When a 
butterfly with one eye blackened, is placed before a window, the 
light conditions resemble, in many respects, those present in 
non-directive light. A change in position on the part of the 
organism, does not involve the illumination of an entirely different 
area of the functional eye. In every position all large areas of 
the eye are approximately equally illuminated, and no two posi- 
tions involve the illumination of entirely different areas of the 
eye, for the sources of reflected light are countless, and extend 
on all sides of the animal. 

No definite conclusion can, however, be drawn as to the nature 
of the stimulus which regulates the movement of the butterflies 
in non-directive light. Superficially it would appear to be due 
to the continuous action of light. Yet, it must be remembered, 
that with every change in the axial position of the butterfly, 
although there may be essentially no change in the illumination 
of the surface of the eye, there must be accompanying changes of 
intensity upon certain of the ommatidia. ‘There is just one 
possible type of reaction in which the same ommatidia would be 
illuminated equally in all of the positions assumed by the insect, 
and that is movement of the organism in a cirele with its center 


404 WILLIAM L. DOLLEY, JR. 


directly below the center of the lamp. But since this did not 
occur, it is evident that there must be changes of intensity of 
light upon certain ommatidia coincident with every change in 
position of the head. 

The fact that some butterflies with one eye blackened, when 
placed in non-directive light, at times moved in a more or less 
straight course, especially when tested twenty-four hours or more 
after the eye was covered, also demands attention. In these 
straightened courses, the movement is either controlled entirely 
or in part by internal factors, or it is the result of a balanced 
effort of two stimuli; one, light, tending to cause the organism 
to turn in one direction, and another, the varnish, tending to 
cause it to turn in the opposite direction. 


E. RELATION BETWEEN THE DEGREE OF CURVATURE IN CIRCUS 
MOVEMENTS AND THE INTENSITY OF NON-DIRECTIVE LIGHT 


If the assumptions made by the adherents of the ‘continuous - 
action theory’ are valid, i.e., if orientation in organisms is depend- 
ent upon the relative amount of light energy received by the two 
retinas, and if the tension of the muscles controlled by the retinas 
varies with the amount of light energy received, then the circles 
made by animals with but one functional eye in non-directive 
light of high intensity should have a smaller radius than those 
made in light of low intensity, for the amount of light energy 
received by the functional eye would be greater in the high in- 
tensity than that received in light of low intensity, and, conse- 
quently, the inequality between the amounts of energy received 
by the two retinas would be greater under the former condition 
than under the latter. 

This was tested in two experiments. In one, non-directive 
light of two fairly high intensities was used; in the other, the 
insects were first exposed to light of very low intensity (0.5 to 
0.07 me.) and then the intensity was gradually decreased. These 
experiments were performed in the light-tight box previously 
described. , In the first experiment the lower intensity was pro- 
duced by placing a 16 c.p. lamp over the opening of the box, and 
by interposing resistance in the circuit until the intensity of this 


TABLE 6 


Behavior of butterflies with one eye blackened, in non-directive illumination of 6 
mc. when tested on several successive days 





OF 
ANIMALS 





(89S Bere & 


(701 Ree 


! 


RA eee a sins.c's 


= 
a 
ne 
| ———. SSS ee ao —_N 


NUMERICAL 
DESIGNATION |ORDER OF DAYS 
ON WHICH 
TESTS WERE 
GIVEN 


oe WS dD 


ow 


BEHAVIOR 





Circus movements; circles 6 cm. in diameter; in several trials it went 
in more or less straight courses for as muchas 18cm. andthen curved 
toward the functional eye 

Not tested 

Not tested 

Continuous circus movements; circles 5 cm. in diameter 

Circus movements; circles 15 cm. in diameter; in several trials went 
in more or less straight courses for as much as 18 em. and then 
curved toward the functional eye 

Circus movements; circles 5 cm. in diameter 





Circus movements; circles 20 cm. in diameter 

Circus movements; circles 5 cm. in diameter; in several trials went 
in more or less straight courses for as much as 10 em. 

Circus movements; circles 6 em. in diameter; in several trials went in 
more or less straight courses for as much as 15 cm. 

Circus movements; circles 5 em. in diameter. 





Circus movements; circles 5 cm. in diameter, in several trials went 
in more or less straight courses for as much as 10 em. 

Same behavior as on first day 

Circles 8 em. in diameter in direction of blackened eye 

Behavior similar to that shown on first day 





Circus movements; circles 4 cm. in diameter 
Circus movements; circles 3 em. in diameter. 





Circus movements; circles 10 cm. and 5 cm. in diameter 

No circus movements made; animal moved in more or less straight 
courses for as much as 15 and 16 cm. and then stopped, showing, 
however, a decided tendency to turn toward the functional eye 

Circus movements; circles 10 em. in diameter; in several trials went 
more or less straight courses for as much as 15 em. 





Circus movements; circles 5 cm. in diameter 

Circus movements; circles 3 cm. in diameter, with sharp turns toward 
blackened eye also 

Circus movements; circles 3 cm. in diameter 


Repeated circus movements 
Four circus movements; circles 2 cm. in diameter; it then went in two 
zig-zag courses, which were each 20 cm. long 


Circus movements; circles 2 cm. in diameter 

Circus movements; circles 10 cm. and 3 cm. in diameter; nine circus 
movements in all; it also made three other trials, in which it went 
in a zig-zag course for as much as 45 cm. 


Circus movements; circles 3 cm. in diameter; in several trials it went 
in more or less straight courses for as muchas 10 cm. 

Not tested 

Not tested 

Circus movements; circles 5 em. in diameter; walked 18 cm. in a more 
or less straight course 





' 401 


402 WILLIAM L. DOLLEY, JR. 


this tendency is in general retained for several successive days, 
although some modification in reactions is evident. This state- 
ment, that there is some change in behavior, is supported by the 
fact that of the nine animals tested on more than one day five 
continued to perform circus movements on the first day of the 
tests, but on succeeding days in some trials went in courses which 
were more or less straight for several centimeters. 





Fig. 17 Reproduction of trails made in trials on thrée successive days in non- 
directive light of 6 mc. by butterfly 7/11-3 (right eye blackened). a, trails made 
in three trials on the first day, b, trails made in eight trials on the second day, 
c, trails made in six trials on the third day. Note that the insect moved in 
rather straight courses on the second day, while on the first and third days it 
usually turned continuously toward the functional eye. 


From time to time throughout the entire period, the animals 
used in the experiment above were tested in a horizontal beam. 
In the beginning some of them made circus movements, and 
some did not, but at the close of the experiment none of them 
made circus movements. This is of great interest, for in non- 
directive light these insects continued to make circus movements 
throughout the.entire period. Under both conditions, only one 


REACTIONS TO LIGHT IN VANESSA ANTIOPA 409 


stimuli may be neutralized by their simultaneous action on the 
organism. 

These experiments in non-directive light of different intensi- 
ties show conclusively that there is no relation between the degree 
of curvature of circus movements and the intensity of the light 
above certain very low limits. They thus support most strongly 
the conclusion reached before, that orientation in Vanessa is 
not dependent upon the relative amount of light energy received 
by the two retinas. ‘ 





Fig. 19 Reproduction of trails made in non-directive light of high intensity, 
460 me., by butterfly 10/13-a (left eye blackened). Compare the preceding figure 
with this one and note that in light of high intensity the animal does not move 
in courses with a smaller degree of curvature than it does in light of low intensity, 
thus exhibiting reactions not in accordance with Loeb’s theory of orientation. 


In addition these results contradict an apparently possible 
explanation of the reactions in the horizontal beam of light. 
Superficially it would seem that these reactions may be due 
simply to a balanced effect of two stimuli acting unilaterally, 
one, light, acting continuously and tending to cause movement 
toward the functional eye, and the other, the covering of the 


THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 20, No. 3 


410 WILLIAM L. DOLLEY, JR. 


blackened eye, tending to cause movement toward the non- 
functional eye. However, the lack of correspondence between 
the size of the circles made and the intensity of non-directive 
light shows that the organism does not respond to differences 
in intensity as would be demanded by this theory. This con- 
clusion is further supported by the fact that a gradual change 
in the intensity of light does not affect the angle of deflection. 
Consequently orientation can not be due to a balanced effect 
of the action of the covering on one eye and the action of light 
on the other. 


F. EFFECT OF ILLUMINATING ONLY ONE EYE 
1. Effect of illuminating the entire surface of one eye 


The experiments described previously in which one eye was 
thrown out of function by being blackened were supplemented 
by others in which one eye was prevented from functioning 
simply by not being illuminated. This was accomplished by 
methods somewhat similar to those used by Holmes and McGraw 
(13). These investigators held insects between the fingers over 
a ‘‘thin horizontal dise rotating on a pivot, like the turntable 
of the microscopist,’’ with the head pointing either toward or 
away from the center. ‘‘An electric light was so placed that 
the rays of light fell upon one side of the body. These insects 
attempted to turn toward the light, and by the action of their 
legs, caused the disc to rotate in the opposite direction. When 
the animals became quiet they could, generally, be caused to 
resume their activity by pulling them slightly backward.” 

Holmes and McGraw draw very decided conclusions from the 
results of these experiments. They say (p. 373): ‘“‘There can 
be little doubt that light exercised a continuous stimulating 
influence upon their [the butterflies] activity. It is not possible, 
we believe, to construe phototaxis entirely in terms of differential 
sensibility. Responses to the shock of transition, whether in 
the direction of an increase or a decrease of stimulus, may play 
a part in the orientation of many forms, but the continuous stimu- 
lating influence of light appears to be, in several cases, at least, 
the factor of major importance.” 


REACTIONS TO LIGHT IN VANESSA ANTIOPA 411 


Feeling that the methods, as described above, were scarcely 
adequate to justify the conclusions drawn, a somewhat similar 
piece of apparatus was constructed with the important modifica- 
tions that the light conditions were sharply defined, and that the 
animals were suspended above the dise by means of a mechanical 
holder, instead of being held with the hand. The object of this 
experiment was to ascertain the nature of the stimulus effective 
in orientation, that is, whether light produces orientation through 
its continuous action or through a change of intensity. A way 
of determining this would be to exclude one of these possible 
methods of stimulation and to test the effect of the other alone. 
Consequently, if the latter method is to be excluded, the organ- 
ism should be so held that it would be subjected to no changes 
of intensity. This condition is met only if the precautions 
deseribed above, or similar ones, are taken. 

That this condition might be fulfilled and that the direction 
of movement of the animal might be detected, a circular piece 
of thin black card board, 10 cm. in diameter, was suspended in 
a horizontal position by means of a hat pin which was held in a 
support that offered as little resistance to the easy movement 
of the pin as possible. To the bottom of the dise a thin cork 
was glued so that the pin pierced the cork as well as the disc. 
The butterflies were suspended above the dise by means of a 
holder which clamped the wings firmly together. The holder 
was then adjusted so that the insects faced the center of the disc, 
and were at such a distance above the disc that they could just 
touch it with their feet, and yet not get a firm grip upon it. 
A Nernst glower was so situated that the rays from it struck 
the right eye of the animal at right angles to the long axis of the 
body. By means of sereens the beam of light was made so small 
that the area of a cross section of it was but slightly larger than 
the surface of the illuminated eye. In line with the glower and 
the head of the animal a mirror was so placed that it reflected 
the shadow of the head of the animal down upon the table which 
supported the whole apparatus, as is shown in figure 20. A screen 
was placed around the image so that as little light as possible 
might be reflected into the room. Under these conditions the 


412 WILLIAM L. DOLLEY, JR. 


head, only, was illuminated. Any movement of the legs of the 
insect could, however, be instantly detected, for, as the legs 
moved the head was ‘bobbed’ simultaneously up and ‘down. 
Thus, by observing the reflected shadow of the head, the periods 
of activity of the animal could be ascertained. 

The results obtained were essentially the same in all of the 
seven experiments performed. They may be illustrated by the 
following detailed description of part of one of them. After the 





























Fig.20 Diagram to show apparatus used in experiments in which the butterfly 
is suspended above a rotating disk. A, Nernst glower; B, disc; C, butterfly; 
D, holder clamped over wings of butterfly; #, mirror. 


butterfly was placed in the mechanical holder, with the right 
eye illuminated by the beam of light, it remained quiet for 390 
seconds; then became active and continued to move for 15 
seconds; after which periods of rest and activity alternated as 
follows: quiet 240—active 10—quiet 60—active 30—quiet 60— 
active 5—quiet 60—active 30—quiet 90—active 5—quiet 60— 
active 120. Whenever the insects were active they attempted 


REACTIONS TO LIGHT IN VANESSA ANTIOPA 413 


to turn toward the functional eye, never in the opposite direc- 
tion. What causes changes from rest to activity, and what is 
the significance of the fact that the animals attempt continu- 
ously to turn toward the functional eye? 

During the periods of rest the changes in illumination in the 
eyes were exceedingly slight for the light remained practically 
constant, and there was no change in the position of the eyes. 
Consequently, if the change from rest to activity is due to light 
at all, which is questionable, since the butterflies do at times 
move in total darkness, it must be due to stimuli dependent upon 
the continuous action of light, not upon the time rate of change 
in intensity. Regarding the nature of the orienting stimulus 
the results are unfortunately not so conclusive, for the moment 
the animals become active, and before they attempt to turn, 
there is a change in the position of the eye owing to the vertical 
movements of the head, and this, no doubt, results in changes 
in the luminous intensity on the various ommatidia. Thus, it 
is evident that the attempt on the part of the animal to turn 
toward the illuminated eye may be due to stimuli dependent 
upon the time-rate of change of intensity. 

Thus, it is clear that these results do not fully settle the ques- 
tion as to how light acts in producing the orienting stimulus and 
that the conclusions of Holmes previously stated are not justified. 

The method described above of exposing one eye only to light 
gives opportunity for testing the effect of illuminating different 
areas of the eye. The results of this experiment are presented 
in the following section. 


2. Effect of illuminating different areas of one eye 


We have demonstrated that in Vanessa only one eye is neces- 
sary in the process of orientation in light. Now the question 
arises concerning the effect of the illumination of different areas 
of the eye. If there is any effect then the axial position assumed 
by the animal ought to bear some specific relation to the area of 
the eye illuminated. 

This was tested by suspending the insects above a disc, as in 
the previous experiment, and by allowing the horizontal beam 


414 WILLIAM L. DOLLEY, JR. 


of light to strike the right eye from different directions. In one 
experiment the beam struck the eye obliquely from the rear as 
is represented by the arrow (a) in figure 21. Thus the posterior 
half of the right eye was illuminated while the left eye was in 
darkness. In another the rays of light struck the right eye 
obliquely from in front, as is represented by arrow (b) in figure 
ZA 

Under the former conditions, when the posterior half of the 
right eye was illuminated, eight animals were tested, each for 
thirty minutes. As in the preceding experiment these insects 
showed alternate periods of rest and activity. During the periods 
of activity they all attempted to turn toward the illuminated 
eye, as was shown by the direction in which they revolved the 
disc.’ 


X 


Ka 
Fig. 21 Diagram to represent the direction from which beams of light were 
allowed to strike the right eye (see text). 


Under the latter conditions, when the anterior half of the right 
eye was illuminated, the animals were also alternately quiet 
and active. When active they varied in their behavior. Some 
attempted to turn toward the illuminated eye, while others 
attempted to turn in the opposite direction. They were tested 
on several successive days, the tests on each day lasting for 
thirty minutes. | 

The first animal (A) tested attempted to turn continuously 
toward the shaded eye on the first day. On the second day, 
during the first part of the test, it attempted to turn in the same 
direction, but during the last part of the test it attempted to 
turn in the opposite direction, i.e., toward the illuminated eye. 


* The dise could not be seen. Its direction of motion was perceived, however, 
by means of a ight paper arrow glued to the bottom of it. The hand of the 
observer was so held that the arrow struck the hand as the disc revolved. 


REACTIONS TO LIGHT IN VANESSA ANTIOPA 


415 


On the two following days it continued to attempt to turn 
toward the illuminated eye. 

The second animal (8) on the first day attempted to turn 
toward the shaded eye continuously. On the second day its 


behavior varied. 


As in the experiments in which one entire 


eye was illuminated, this animal without any perceptible change 


TABLE 9 


Showing direction in which eight butterflies attempted io turn on successive days when 
the anterior surface of the right eye was illuminated obliquely from in front 


DESIGNATION OF 
ANIMALS 


B 





tc) 


F 





7 


— 








ee — eS Se = = 





FIRST DAY 


Away from il- 
luminated 
eye 


Away from il- 


luminated 
eye 


Toward — illu- 
minated eye 


Away from il- 











SECOND DAY 


Away from il- 


luminated 
eye 


Away from 1l- 
luminated 
eye and to- 


ward _ this 
eye 
Toward | illu- 


minated eye 





Toward | illu- 
luminated| minated eye 
eye 

Toward illu-| Not tested 


minated eye 


Toward  illu- 
minated eye 
(Most cases) 


Away from il- 


luminated 
eye at first; 
then toward 
illuminated 
eye 


Away from il- 
luminated 
eye 


Toward illu- 
minated eye 


Away from il- 


luminated 
eye in most 
cases 


Toward illu- 
minated eye 


THIRD DAY 


FOURTH DAY 











Toward illu- 
minated eye 


Toward illu- 
minated eye 


Toward  illu- 
minated eye 


Toward © illu- 
minated eye 


Not tested 


Toward illu- 
minated eye 





Toward  illu- 
minated eye 


Toward  illu- 
minated eye 





Not tested 











Toward illu- 
minated eye 


Not tested 


Not tested 


Not tested 


Toward  illu- 
minated eye 





Toward  illu- 
minated eye 


Not tested 








416 WILLIAM L. DOLLEY, JR. 


in the environment exhibited alternate periods of activity and 
rest. Forty periods of activity were observed during the test. 
In fifteen of the first twenty of these it attempted to turn away 
from the illuminated eye, while in fifteen of the last twenty it 
attempted to turn in the opposite direction. On the third day 
it attempted to turn toward the illuminated eye uniformly. 

In table 9 the results secured with the eight animals used in 
these tests are summarized. | 

By referring to this table it will be seen that when the anterior 
surface of only one eye is illuminated Vanessa usually turns 
toward the shaded eye when first exposed, but that later it turns 
consistently toward the illuminated eye. Consequently, since 
it always turns toward the illuminated eye when the posterior 


surface is exposed, it is evident that the reactions may depend 


to some extent upon localization of the photic stimulus in the 
eye. 

The results presented in this section show, moreover, that the 
tension of the muscles in the legs on either side is not specifically 
dependent upon chemical changes in either eye, as demanded 
by the ‘continuous action theory,’ for without any change in 
the illumination of a given surface of one eye the animal may 
turn either to the right or to the left. 


GENERAL SUMMARY AND CONCLUSIONS 


1. Vanessa antiopa creeps and flies toward a source of light, 
that is, it is positive in its reactions to light, never negative. 

2. Butterflies of this species, in direct sunlight come to rest 
with the head away from the source of light. 

3. When placed in a horizontal beam so as to face the light 
Vanessa with one eye blackened usually turns toward the func- 
tional eye. In some cases it continues to turn in this direction 
and consequently performs circus movements both in the beam 
and in the shaded region beyond it; usually, however, it proceeds 
in a fairly straight course diagonally across the beam until the 
edge of the beam is reached, where it usually turns toward the 
covered eye and moves directly toward the source of light. Some- 


Oe 


REACTIONS TO LIGHT IN VANESSA ANTIOPA 417 


times the insect does not turn toward the source of light until it 
has gone a few centimeters beyond the edge of the beam. The 
angle through which the butterflies turn before they proceed 
toward the edge of the beam, varies in different individuals and 
in the same individual under different conditions. Moreover this 
angle bears no observable relation to the luminous intensity. It 
was found to be the same in 200 me. as in 2000 me. 

4. In non-directive light, or before an open window, these 
insects move in circles toward the functional eye, and continue to 
do so, showing no apparent improvement. This is probably due 
to the absence of changes of illumination on the surface of the 
eye. Thus, the performance of circus movements is, in many 
cases dependent upon the approximately equal illumination of 
large areas of the functional eye in all the positions assumed by 
the organism. 

5. Cireus movements, however, throw no light on the nature 
of the stimulus effective in orientation, for the slightest change in 
position of the head may produce changes of intensity on certain 
ommatidia in the functional eye. 

6. Vanessas with one eye blackened do not move in smaller 
circles in strong light than they do in weak light, unless it is 
extremely low.. On the contrary, the evidence seems to indicate 
that the stronger the light is the larger the circles are. These 
results also are not in harmony with those demanded by the 
‘continuous action theory.’ 

7. If, however, the intensity of non-directive light is made very 
low, Vanessa with but one functional eye deflects neither to the 
right nor to the left, and, if it is made still lower, it moves in 
circles toward the blinded eye. 

8. These animals modify their behavior as the result of repeated 
trials. This modification in reactions is shown in three respects: 
(1) decrease in the number of circus movements made, (2)decrease 
in the angle of deflection and (3) increase in the promptness with 
which they orient on reaching the edge of the beam. 

9. If the luminous intensity is suddenly changed when speci- 
mens of Vanessa antiopa with one eye blackened have oriented in 
a beam of light, and are moving toward the source of light at a 


418 WILLIAM L. DOLLEY, JR. 


certain angle with the rays, the response varies. Usually, how- 
ever, if the luminous intensity is suddenly increased the butter- 
flies increase the angle of deflection, and if the intensity is sud- 
denly decreased, they decrease the angle of deflection. These 
results are probably dependent upon the time-rate of change and 
are not due to the difference in the amount of light energy received 
by the functional eye under the different conditions. 

10. Vanessa antiopa with one eye blackened can re-orient. If, 
when the animal is moving toward a source of light, the direction 
of the rays is changed so that the light strikes the butterfly on 
the side of the blinded eye, the organism changes its direction of 
motion by turning directly toward the source of light. If the 
source of light is moved to the other side of the animal, the 
butterfly again changes its direction of motion and goes toward 
the light. Thus, with one eye functional, the animals in orient- 
ing may turn either toward the side bearing the functional eye, 
or toward the side bearing the blinded eye. ‘These results con- 
tradict the assumption of the ‘continuous action theory,’ that 
orientation is dependent upon the relative amount of light energy 
received by the two retinas. 

11. Specimens of Vanessa with one eye blackened move in 
circles toward the blinded eye when placed in darkness, while in 
light they tend to turn in the opposite direction. This shows 
that the covering of the blackened eye produces a stimulus. It 
also shows that the circus movements toward the functional eye 
in the presence of light are due to a stimulus produced by light, 
and are not due to stimuli received by the blinded eye. 

12. When suspended above a rotating dise with the head 
pointing toward the center of the disc, and with only one eye 
illuminated, Vanessa attempts to turn toward the illuminated 
eye. Under such conditions there are alternate periods of rest 
and activity. The stimulus initiating a period of activity is not 
due to change in luminous intensity, and hence it must be due 
either to internal factors or to the continuous action of light. 

13. If, however, the light is so arranged that only the anterior 
surface of the right eye is illuminated, the animal may turn 
either to the right or to the left. This indicates that the reac- 


REACTIONS TO LIGHT IN VANESSA ANTIOPA 419 


tions may depend upon the localization of photic changes within 
the eyes, and it seems to show conclusively that the tension of 
the muscles of the legs on either side of the body is not specifi- 
eally controlled by photo-chemical changes in either eye in 
accord with the ‘continuous action theory.’ 

14. The following facts: (1) that Vanessa antiopa with but one 
eye functional can orient, (2) that in a beam of light circus move- 
ments become less frequent and the angle of deflection decreases 
with experience, (3) that the degree of deflection is no greater in 
light of high intensity, than it is in light of low intensity, (4) that 
Vanessa can turn under certain conditions toward either side 
when only one eye is illuminated, and (5) that these insects can, 
in the process of orientation, turn either toward the functional 
or the blinded eye, all, indicate that orientation in Vanessa is 
not wholly dependent upon the relative intensity of light on the 
two eyes. They show moreover that the path in the nervous 
system along which the impulses travel is not permanently fixed. 
Regarding the question as to the nature of the orienting stimulus 
our evidence is, however, not conclusive. 


BIBLIOGRAPHY 


Barrows, W. M. 1907 The reactions of the pomace fly, Drosophila ampelo- 
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537. 

Boun, G. 1911 La Nouvelle Psychologie Animale. Paris. 

BrunpIn, THorBoRG Marie 1913 Light reactions of terrestrial amphipods. 
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Carpenter, F. W. 1903 Reaction of the pomace fly, Drosophila ampelophila 
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1908 Some reactions of Drosophila, with special reference to convul- 
sive reflexes. Jour. Comp. Neur. and Psych., vol. 18, pp. 483-491. 

Hapuey, Puitre B. 1908 Reaction of blinded lobsters to light. Am. Jour. 
Phys., vol. 21, pp. 180-199. 

Houtmes, 8. J. 1901 Phototaxis in the amphipoda. Am. Jour. Phys. 
pp. 221-234. 
1905 The reactions of Ranatra to light. Jour. Comp. Neur. and 
Psych., vol. 15, pp. 305-349. 
1905 The selection of random movements as a factor in phototaxis. 
Ibid., vol. 15, pp. 98-112. 
1911 The evolution of animal intelligence. New York, pp. 280. 
1912 The tropisms and their relation to more complex modes of 
behavior. Bull. Wis. Nat. Hist. Soc., vol. 10 pp. 13-23. 


MaVOl wo. 


420 


WILLIAM L. DOLLEY, JR. 


Houmes AND McGraw K.W. 1913 Some experiments on the method of orienta- 


tion to light. Jour. Animal behavior, vol. 3, pp. 367-373. 


Jennines, H.S. 1906 Behavior of the lower organisms. New York, 366 pp. 
Keuioae, V. L. 1907 Some silkworm moth reflexes. Biol. Bull. Vol. 12, pp. 


Logs, 


UE 


152-154. 

1888 Die Orientierung der Thiere gegen das Licht. (Thierischer 
Heliotropismus). Sh. d. phys. med. Ges., Wurzburg, pp. 1-5. 

1889 Der Heliotropismus der Thiere und seine Ubereinstimmung mit 
dem Helotropismus der Pflanzen. Wiirzburg. 118 pp. 

1900 Comparative physiology of the brain and comparative psychol- 
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1905 Studies in general physiology. Chicago. Vol. 1, 423 pp. 

1906 The dynamics of living matter. New York, 233 pp. 

1907 Concerning the theory of tropisms. Jour. Ex. Zoél., vol. 4, pp. 
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1909 Die Bedeutung der Tropismen fiir die Psychologie. Liepzig, 51 
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1912. The mechanistic conception of life. Chicago, pp. 227. 


Mast, $.O. 1907 Light reactions in lower organisms. II. Volvox. Jour. Comp. 


Neur. and Psych., vol. 17, pp. 99-180. 

1910 Reactions to light in marine turbellaria. Carnegie Institute of 
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1911 Light and the behavior of organisms. New York, pp. 378. 
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1915 What are tropisms? Arch. f. Entw. Mech. Bd. 41, 8S. 251-263. 
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RADL, 


Ki. 


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1901 Uber d. Phototropismus einiger Arthropoden. Biol. Cent., 
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Ka 


VITA. 





William Lee Dolley, Jr., was born near Staunton, Va., April 
13, 1887. He entered Randolph-Macon College in 1904 and 
was graduated in 1907 with the degree of A.B. In 1908 he 
was Instructor in Latin at that Institution, and received the 
~ degree of A.M. He attended the Johns Hopkins University 
during 1909-1910 and 1911-1914, making Zodlogy his princi- 
pal subject of study, Botany his first subordinate and Physi- 
ology his second subordinate. In 1908-1909 he was Instructor 
in English in Randolph-Macon Academy, Front Royal, Va. In 
1910-1911 he was Instructor in Biology in Western Reserve 
University. In 1911-1913 he was Student Assistant in Gen- 
eral Biology and Embryology in the Johns Hopkins Univer- 
sity, and in 1913-1914 he held a graduate scholarship. 











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